The evolution of the Internet has led to the creation of new communication and work tools for businesses as well as for individuals. This thesis will look at a specific category of these tools: social networks. We must differentiate between non-virtual social networks, which have existed for centuries (belonging to a political party, a sports club, a fraternity, a religion, a bridge club, etc.), and online social networks , which are exclusively based on the use of the Internet.

Web 2.0 has brought the evolution of social networks. They are increasingly used by Internet surfers, and they reach an extremely wide audience. Students and teens were the first users of such sites, making them the precursors of today's social networks. It should also be known that currently, for many users, using these sites is considered a social activity in its own right. Today, there are [1] no less than 1.43 billion social network users worldwide in 2012 (19% more than in 2011), and we expect growth of up to 1.85 billion users assets at least once a month in 2014. This amplification makes social networks a leading market, which can no longer be ignored by companies.

The business world quickly realized the interest of using social networks, for financial purposes and promoting the management of their e-reputation [2]. Some companies have decided to use them for business purposes, in order to involve their employees and sometimes their customers in the life of the company. Today, all businesses are dealing with social networks, which allow them to manage their image, develop financially and enrich their experience in the web market that offers new opportunities, previously nonexistent. Creative employees are having a blast and new jobs have emerged with the advent of web 2.0: social media manager, community manager, social media application manager, web content manager or search engine marketing specialist [3 ].

In addition to their role in computing, social networks have a sociological dimension. Even before the fashion of social networks on the Internet, the notion of network knew indeed in social sciences a growing success since several tens of years. In his book "The sociology of social networks", Pierre Mercklé [4] explains that "the pioneering work of Jacob Moreno, Stanley Milgram, anthropologists of the Manchester School (John Barnes, Elizabeth Bott ...) or sociologists of Harvard group (Harrison White, Mark Granovetter ...) have brought out a whole set of concepts, models and empirical research, constituting this "sociology of social networks": it is to take as objects of study not the characteristics of individuals (age, gender, occupation, etc.), but the relationships 

between individuals and the regularities that they present, to describe them, account for their formation, their transformations, and analyze their effects on behavior ". However, this thesis will not focus on the study of the sociology of online social networks, but will focus exclusively on their concrete uses and the consequences of their use in the context of web 2.0.

This document will attempt to answer the following problem: "Does the impact of social networks on businesses play a key role in their image? ". To do this, we will first explain the role of online social networks and explain where they come from. In a second part we will study the consequences of social networks on companies, the obligationa necessary adaptation which will offer them new opportunities but also potential risks. Finally, in the third part, we will answer the problem directly by analyzing the direct consequences on businesses and consumers, and then we will finally ask ourselves whether social networks are indispensable or not to the vitality and durability of the companies that use them. .

This thesis has been realized thanks to various research questions, of which the main ones are:

• What are the main social networks used by companies?
• What are the risks if there are more and more social networks?
• Are there adequate staff training in each company on the use of these ICTs?
• What is the link with advertising?
• Can companies control all computer buzz?
• Should companies focus on social networks (external) or internal networks of companies?
• What other real or virtual carriers of companies to maintain its image?
• Is the presence of companies on social networks vital?
• How are companies using these networks to their own advantage?
• Where does freedom of expression and communication of companies stop on social networks?
• Could businesses grow as easily if social networks had never existed or disappeared?

A. The role of social networks

       I. The arrival of web 2.0

The end of the 80s is accompanied by a revolution in the field of computer and Internet developments. Tim Berners-Lee, a member of CERN Geneva, proposes to develop a hypertext system organized in "Web" by writing an HTML code (a computer language for writing data to represent pages on the internet), in order to to improve the dissemination of internal information: it is the creation of the "World Wide Web" (also called "WWW", "Web" or "W3") and the birth of a brand new mode of communication and exchanges data and information.

This has led to the creation of a multitude of websites (most of which are still used today), the development of new computer languages, the creation of the first software and first browsers such as NCSA Mosaic, Lynx, Microsoft Internet Explorer, Netscape or Mozilla. The Web recorded 26 sites in 1992, more than 600 sites in 1993, more than 10000 sites in 1994 and no less than 45 million sites in 2004. The Web has become a virtual platform where companies buy software developed by others for billions of dollars and where there is a very competitive atmosphere.

In the mid-2000s, the concept of "Web 2.0" appeared. Spread by Tim O'Reilly in 2004, this new web is supposed to facilitate the access to the information to the users having little technical knowledge to appropriate the new functionalities of the web. Indeed, the notions of communication are becoming popular, thanks to the widespread use of blogs, sites dedicated to free information called "wiki pages" (Encarta in 1993 then Wikipedia in 2001) and of course thanks to the appearance social networks such as Myspace in 2003, Facebookin 2004, etc. The content generated by users is spreading and the concept is popularized at a very high speed from 2005. The new "consum'actors" are very fond of this new conception of the web because they can use their freedom of expression, share their creativity, their knowledge or their experiences on the internet in an extremely simple and fast way, in the eyes of all or not. They are now actors of the web, and no longer have to browse the Internet passively, without the possibility of sharing with the world what they do or think. In addition, many software companies offer on their site, for free, quick and easy to edit images, edit videos ... Previously,

In his article "The Web at Power 2: Web 2.0 Five Years Later," Tim O'Rilley notes in 2009 that "Web 2.0 is about harnessing collective intelligence," especially with the emergence of community-based Web sites. such as Youtube, Facebook and Twitter because users are looking for value created by and for their community. According to the principle of "power law of participation" Ross Mayfield, we went from a collective intelligence (read, save a bookmark ...) to a collaborative intelligence (write, moderate ...). Indeed, Are there people today who do not try to integrate communities to talk about topics that interest them or to share their views or behaviors with Internet users who have the same passions as them? And the computer revolution has even been to the stage of the appearance of smartphones, which has moved the web from our offices to our pockets. Collective intelligence applications are no longer just activated by humans typing on keyboards, but, increasingly, by sensors. Phones and cameras become the eyes and ears of apps; motion and location sensors tell where their users are, what they're looking at, how fast they're moving ... Collective intelligence applications are no longer just activated by humans typing on keyboards, but, increasingly, by sensors. Phones and cameras become the eyes and ears of apps; motion and location sensors tell where their users are, what they're looking at, how fast they're moving ... Collective intelligence applications are no longer just activated by humans typing on keyboards, but, increasingly, by sensors. Phones and cameras become the eyes and ears of apps; motion and location sensors tell where their users are, what they're looking at, how fast they're moving ...

In addition to benefiting many individuals, the web 2.0 is of vital utility for companies looking to venture there. Indeed, this tool offers:

• services, not a software package, with economies of scale
• control over unique, hard-to-recreate data sources that increase in richness as people use them
• considering users as co-developers
• the ability to leverage collective intelligence
• access to the market even in its periphery through the establishment of "ready to consume" services
• flexibility in user interfaces, development models and business models.

In addition to opening new business sectors for companies, they can use web 2.0 to maintain their image, but also to pose barriers to the actions of consumers and employees. For example, they have the opportunity to regularly update their website, their blog and their news on social networks through community managers, but also to regulate the content of blogs when talking about them, and more and more to check what publish their (future) employees on social networks. They have the possibility of having recourse to the justice to avoid that Internet users tarnish their image, the goal, of course, is to propagate the cleanest possible image while being aware that it is easy to attack the reputation of a company on a ground where everyone can express themselves freely. It should also be noted that all areas of activity are likely to be criticized on the internet thanks to this freedom of expression, whether towards a personality (for example a politician), an opinion (such as abortion or homosexual marriage), an event (a concert or an event), an artistic realization (a drawing, a photo or a video), etc.

    II. The emergence of electronic social networks

        i. What is a social network?

The term social network was introduced for the first time in 1954 by John A. Barnes, a member of the Department of Social Anthropology at the University of Manchester, in an article by Human Relations, an English monthly on the social sciences. As explained by Pierre Mercklé [5], "Barnes' goal is to account for the social organization of a small community, through the analysis of all the relationships that its members have with each other. others ". To do this, he distinguishes three social "fields": the first, based on a territorial base, comprising the administrative units and the voluntary associations, corresponds to the political organization and is characterized by a certain hierarchy and a great stability; the second, corresponding to the industrial system, essentially organized around fishing; finally, the third social field, without well-defined boundaries, refers to the set of informal relations between formally equal individuals, acquaintances, friends, neighbors or parents.

A more modern definition of a social network appeared in 2004 as "a set of relationships between a set of actors" [6]. This set can be organized (it is the case of a company) or not (like a network of friends) and these relations can be of very different nature (power, exchanges of gifts, advice, etc.), specialized or no, symmetrical or not. It is an immaterial element that defines the interaction between elements or persons who belong to the same group with a view to their commonalities, material or immaterial.

According to Danah Boyd and Nicole Ellison, social networking services can be defined as Internet services that allow their users to:

• To build a public profile as part of a delimited system
• Organize a list of users with whom they share different relationships
• See and cross his lists of relationships but also those of other users who are in the system.

To survive, a social network must generate interdependence among its members. They need to share their experiences and get feedback from other members, in other words their reactions. These experiences can be in the form of information, articles, videos or images. This distribution of more or less personal information is directly related to the growth of free culture , whose web 2.0 allowed the flight.

In practice, there are classically 4 major types of networks:

- networks of old (buddies before)

- looking for a soul mate (Meetic, Match.com)

- the development of the professional network (LinkedIn, Viadeo, Plaxo, Xing ')

- services dedicated to exchanges and socialization between people with common affinities (Facebook, VKontakte, Myspace, Fourquare, Flickr).

     ii. Diversification of free culture

Free culture can be defined [7] as "the free distribution of knowledge and its growth through the development, modification or enrichment of already existing works on the basis of sharing and collaboration without these are hampered by the rules relating to the legal protection of intellectual property ". It advocates equal access to information and knowledge and is prior to the invention of the internet. Indeed, in 1911, Henry Ford undertook to cancel the patent that George Selden of Rochester filed in 1895, which gave him exclusivity for two-stroke engines and which hampered the development of the automobile in the United States. Having won, Ford created what would become the Motor Vehicle Manufacturers Associationin which the manufacturers freely used their reciprocal patents. Thus, each car company was free to develop its own technologies and to obtain the appropriate patents, which could be used by all the companies of the group without having to pay a fee. It is this same idea of ​​sharing based on the work of each other that is the basis of free culture in the field of computing. The values ​​it supports are: freedom, freedom of expression, user control, privacy, sharing of knowledge and coopetition [8].

The best example to illustrate this philosophy on the Internet is undoubtedly the Wikipedia, universal electronic encyclopedia put online on January 10, 2001: more than 16 million articles written in more than 270 languages ​​and attracting some 78 million visitors. Today, not less than 300 million photos are shared every day on social networks [9].

It is important to differentiate between free computer culture and the free culture of Internet users. The free computer culture is recounted by "free software", which advocates free sharing of source codes (with however some restrictions from copyright), while the free culture of Internet users is their desire to share photos or videos on the web, with a notion of free. Indeed, a lot of Internet users download movies, music, or images for free then share them without worrying about the copyright to which these elements are subject. To counter this, several states, including France, seek to have laws to strengthen the market dimension of the Web. The best known law in France today is certainly Hadopi, created in 2009,

   iii. The ease of access to information

The advent and development of web 2.0 have dramatically changed the access to information of Internet users. Today, anyone can get the information they want in just a few clicks, thanks to the 580 million sites [10] of which the web is composed. In addition to the increase in the number of daily sites (recorded at 60,000 new sites per day [11]), there is an increase in the number of Internet users. In France, the sites on which Internet users like the most to navigate are Facebook, Leboncoin, Google , MSN, Youtube and Ebay. French Internet users spend each month a time of up to 5:26, 2:15 and 1:48 respectively, for the first three sites [12]. Their most popular activities when they sail are the sale and rental of real estate, cars and second-hand goods. The websites involved average 500,000 information updated daily.

Moreover, it is clear that Web 2.0 and social networks are at the heart of a revolution in teaching and learning. More than ever, students have access to collaborative environments that promote the sharing and co-construction of knowledge (Elgg, Ning, Wikis, etc.). More flexible, the Web 2.0 technology tools offer learners greater control and promote the emergence of personal learning spaces. Sites like Wikipedia, Del.icio.us, YouTube and iTune U contain more and more content and approaches that can enrich the learning experience, even though these sites were basically created for a purpose not lucrative.

At the beginning of the 90s, it was easier to search for information because it was listed in computer directories and it was enough to find the information where it was kept, as if it were searched in a tidy book. in a library with good shelving. Today, the mass of sites available has become disproportionate, and we see that no one is looking for information in computer directories (the little that remains are no longer updated [13]). This change in the storage of information was well illustrated by two videos of Michael Wesch, a professor at the University of Kansas, created in 2007. The first, "The Machine Is Us / ing Us" [14], explained the appropriation and linking Web content by Internet users, while the second, "Information R / evolution",

It is therefore extremely easy today to have access to information on the Internet, whether in the form of text, photo, video, location (thanks to the features of Google Maps, Google Earth, Mappy or still Flickr Maps). It is enough to know where to look for it and to be able to filter the correct or erroneous information (also called "hoax" [16]). Because if today, an average surfer is able to post information on the internet, it is not excluded that they are true every time. We can again quote the example of Wikipedia, the free universal encyclopedia that allows any user to publish information, which submits the writers to the rules of the Creative Commons license, which allows them to "share,

 III. The different types of communication

        i. Internal communication

Internal communication is communication within the company. Without the latter, such a communication would not exist. It is the managerial direction of the company that assigns him a role and a budget. From a purely hierarchical point of view, internal communication is generally attached to one of the following three entities:

• The human resources department  : the media is closer to its target
• The communication department  : in this case, the internal communication is linked to the external communication since the direction of the communication is closely linked with the management of the company
• General management  : here, external communication is directly linked to the company's strategy.

Communication has been an important event for several decades. As explained above, people want to "let others know" what they think, what they like by sharing data on social networks. The situation is very similar in the business world, where more and more means of communication between employees exist, be it corporate communications, internal sources of information such as e-mails, bulletin boards, welcome booklets, retro-planning, etc. but also media from third parties such as associations, business partners, unions or committees. In his memoir "The internal communication of the company", Jean-Baptiste Brès [18] explains that "this communication is formed above all around a need for identity. This identity allows its employees to know how to behave within it and its partners to distinguish it from another company. " In other words, it regulates the life of the company to coordinate the relations between the different layers of its hierarchy.

This communication can be oral or written. The oral means correspond to all the vocal supports put in place by the management to inform the staff of the changes of the company, to have feedback on the impressions of the employees or to know the state of mind of the teams working on a project: meetings, internal events, seminars, collective or individual interviews. Written means, asto them correspond to all the manuscripts or computer supports that are readable by employees: company newspaper, welcome booklet, press reviews, posters, brochures or brochures, documentation, intranet, company blog, newsletters, page on social networks such as Facebook, Twitter, Viadeo, LinkedIn, etc. Companies are also increasingly using e-learning [19], a self-learning method that reduces their training costs. Note that the media written on the Internet are readable by employees and by customers or prospects, so they are straddling between internal and external communication.

We are seeing more and more companies using one or more corporate social networks (CSRs). It is an internal corporate social network that, like a public social network, brings together business members in different communities for business purposes and is linked by application platforms. (bringing together employees, customers of the company, its shareholders, partners, etc.). This type of network can significantly strengthen the company's business and help identify the knowledge of its staff.

     ii. External communication

External communication brings together all the company's communication actions aimed at external audiences [20]. It can address customers, prospects or suppliers, who form their opinion and their attitude towards the company. It consists of various actions such as lobbying, media relations, events, sponsorship, sponsorship, the company's website, e-communication, sales promotion, direct marketing and is directly linked to advertising. Companies must control this communication to confirm their image with third parties so that it is as positive as possible. This communication also focuses on the value of the product or service created by the company in the eyes of consumers.

The advent of the Internet has considerably modernized this communication on computer and electronic media. Now, all companies are trying to extol the merits of the goods and services they offer on their website, and maintain the best they can their relations with their customers on social networks. These are the new tools essential to the company if it wants to expand its prospecting target, which mainly concerns the Generation Y [21]. You have to realize that social networks are not online sales sites like eBay, Amazon, Leboncoin or Spartoo, but they are used by companies to communicate more easily with Internet users who "follow" them and to collect their impressions, also called "feedback". The only problem with public social networks for businesses is that members of these networks have to fetch the information themselves (for example I have to choose to follow the activities of Red Bull on Facebook, Red Bull does not come to me ). That is why it is sometimes difficult for young companies or artists to make themselves known on social networks, unless to make the "buzz" [22] (we can mention the thundering success of the short series Bref on