Recently, Roger Thompson, chief research officer at security firm AVG, discovered over half a dozen Facebook applications that had been compromised by malicious hackers. Although the apps' reach was small with relatively few users being affected, Thompson was concerned because it was the first time he had seen apps themselves hacked as opposed to something like Facebook profile pages, a common target for the still-spreading Koobface worm.

While this incident alone wouldn't generate much excitement given the low-profile nature of the applications affected, it's not the only example of unsafe applications on Facebook. Another researcher just spent an entire month scouring Facebook apps for security vulnerabilities and what he found is disturbing: six of the hacked apps were in the top ten, 9700 applications were affected, and the potential victims totaled 218 million users.
How Safe are Facebook Applications?