This week we discovered a large malware spam campaign that used the Zbot Trojan executable. It started with a Voice Message/MMS Service spam message yesterday at around 3:30AM GMT.
The spam uses any of the following subject lines:
The HOTFIX "Important SystemUpdate" spam campaign followed at around 6:00AM GMT. The email claims to be from various anti-virus companies urging the users to install the attached "system patch".
The subject lines used by this spam campaign:
A third spam campaign followed suit, this time using the subject line format, "DHL Delivery Status #[10 hexadecimal char]".
Our spamtrap timeline shows a sudden peak of activity involving these spam campaigns, and then just as suddenly, a decrease. This shows how quick a spammer can change their spam campaign over time.
These three spam campaigns were sent by the same botnet that we suspect is a variant of a Cutwail spambot. The attached files are an executable of a Zeus variant. It copies itself to the %appdata% directory then injects itself into Explorer.exe. It also adds an autorun registry to execute itself on Windows startup. Once installed in a victim's machine, the Zeus Trojan acts as a client that receives commands from its command-and-control server. The botnet operator can then send instructions such as sniffing a user's bank transaction. Our detailed analysis of the Zeus Trojan can be found in this page.
Trustwave's Secure Email Gateway customers were protected from this spam campaign without any additional action required.