( CNN ) -- Users of social-networking sites such as Facebook risk losing control of their personal information because they are not fully aware of the implications for their privacy , a freedom of information expert warned Wednesday . Facebook was forced to revert to its old user-ownership policy following a backlash from users . Data-protection specialist Mark Gleeson told CNN that social networking users should be very careful about what information they post on the Web . He said users should make sure they understand who could access their profiles , and how that information could be used . They also should familiarize themselves with sites ' privacy options , he said . `` It is very important to take steps yourself to understand what is going on with your personal information , '' Gleeson said . `` Once it 's out there it 's very difficult to get it back . You can lose control over it . '' Facebook , currently the world 's most popular social-networking site , was forced to back down Wednesday after many members revolted against a change to its user information policy , which would have granted the site permanent rights to all photos and postings even after a user had closed down an account . But Gleeson , of UK law firm Addleshaw Goddard , said the case raises other issues of privacy concerning social networking , such as the security of personal data and whether information could end up in the hands of marketing companies . He also said that employers have been known to visit such sites to check personal details about prospective workers . Young people , for whom communicating with friends via social-networking sites is often second nature , should be particularly careful about what they post online , Gleeson said . `` They do n't have the level of suspicion that other people have about the Internet because they just see it as a way to communicate and understanding the implications wo n't be in the forefront of their minds , '' he said . Gleeson said the Facebook backlash may have blown up out of a misunderstanding over the site 's attempt to clarify content ownership . But he said the way the company went about the change provoked alarm among some users of the site . `` It comes down to how you deliver the message , '' Gleeson said . `` If you change your terms and conditions and remove a section and leave it at that without bringing it properly to people 's attention you 're going to get suspicion . '' iReport.com : Your thoughts on Facebook 's about-face . Data-protection laws differ from country to country . But Gleeson said Web sites generally face a balancing act between meeting their legal requirements to explain their policy towards personal information -- often in the form of dense terms and conditions pages written in `` legalese '' -- and providing the same information in a way accessible to users . `` One of the requirements of data protection is that personal information is processed fairly and lawfully . Fairness is all about telling people what you are going to do with their information and being clear and transparent , '' Gleeson said . `` The difficulty is that in many cases you 've got a tension between insuring that you tell people what you need legally to tell them against making that clear and understandable . '' iReport.com : Too much information posted online ? But Gleeson said it was in sites ' interests to treat their users fairly . He said the Facebook case demonstrates that social-networking services need to keep their users on their side -- or risk losing them to rivals . `` It 's always in the interests of reputable sites to treat information fairly and treat their users fairly because the last thing you want to be seen to do is alienate people , '' he said . `` When people feel that they ca n't trust a site then they will go elsewhere . ''
Expert : Social - networking site users risk losing ownership of personal information . Google backed down from changing content ownership policy after user revolt . Sites have to balance legal issues , making policies on data privacy clear . Young people in particular should be careful about what they share online .