It is no surprise that Facebook is vulnerable to attacks, and several hackers actively alter people’s profile information, on daily basis. There are hundreds of examples of this. Many Facebook and ex-Facebook users can tell you that they noticed change in their profile information while they were not logged in.
Also, lots of pictures are uploaded on Facebook every day. Yes, Facebook does check every upload for viruses but remember Facebook or any other website can’t check for all kind of viruses, particularly those which are recently released. On opening those virus-attached pics, you create danger to your data and your computer.