The next time Facebook sends you an email about a friend tagging you in a new picture, be cautious -- it could be a trap.

A new strain of malware identified by security firm Sophos as Troj/Agent-XNN has been circulating the social networking site, encouraging members to view photos as an attachment. After clicking on the infected link -- which is disguised as a Facebook notification email -- a ZIP file containing malware allows hackers to gain control over Windows-operated computers.