A number of games and other applications built to be used on Facebook.com have been hacked so that users are quietly sent to sites that try to install malicious programs, a security researcher has found. Roger Thompson, chief research officer for computer security firm AVG, discovered about a half-dozen Facebook games and app home pages had been compromised by attackers. While hacked Facebook profile pages are not uncommon -- thanks largely to threats like the Koobface worm -- Thompson said this was the first time he'd seen actual Facebook applications being hacked. According to Thompson, the hackers somehow slipped malicious "iframes" -- small, hidden chunks of computer code that invisibly load content from exploit sites -- into each of the Facebook.com Web pages where users would go to use the apps. The exploit sites in turn try to foist malicious software if the visitor is running outdated Adobe products, such