Symantec: Yontoo is a potentially unwanted application that installs a browser extension to display advertisements which appear to be from Facebook.
http://www.symantec.com/security_response/writeup.jsp?docid=2012-052923-1931-99 (Dashke posted the link already).
@ ZOU1
The question is, is this something you actually need to have on your machine ?
If not then delete it, Yontoo is fairly harmless as others have indicated, just adware.
Not at all, and even if I thought I was infected, "afraid" is the last thing I am. I run sandboxed and even if I lost my OS it is more than 10 years old with no crucial data on it so.........Besides, I always have access via another computer to download the Dr. Web Live bootable, or KBRD. I simply run Dr. Web CureIt on-demand once every week or two since I have no traditional AV, though I mostly scan with it to sniff out any worms that might be on the network.
I run HitMan Pro too, about every day. For less than a 3 minute wait, you cannot beat it. The first thing I do when I think I am infected is run HitMan and check the view in Process Hacker. That gives me good piece of mind in under three minutes. If I still think I am infected I will use ComboFix or KBRD and scan "users" and "boot sectors". Then I will use Dr. Web CureIt and MBAM to clean up the rest.