Malicious spam messages generated by the infamous Cutwail botnet are targeting Facebook users as potential banking Trojan victims.
The messages arrive in the guise of a Facebook friend invite notification. The emails look genuine enough on casual inspection, thanks to the malware-spinners' apparent use of a genuine Facebook template. But where a genuine Facebook invite contains links to the real social networking site, the malicious emails feature custom links to malware sites. In addition, the emails differ from the genuine article because they do not feature Facebook profile photos. The recipient's email address is also absent from the fine print at the bottom of the bogus invites.
Users tricked into clicking on the malicious link are exposed to a double-barrelled malware based attack. Firstly they are offered a bogus Adobe Flash update. In addition, clicking on the link opens a hidden iFrame, which then loads data from a remote server hosting the Blackhole Exploit Kit. The exploit kit attempts to exploit browser security holes, most notably involving insecure Java installations.
Both techniques attempt to download a variant of the infamous ZeuS banking Trojan onto compromised systems. Impersonating email notifications from Facebook is a common enough technique among spammers and purveyors of survey scams, but we've never seen it applied to punt banking Trojans before.
A full write-up of the scam can be found in a blog post by M86 Security here. ®