Cybercrooks are upping the ante by loading malware as an attachment inside another attachment in a bid to slip past security defences.
A new variant of the Upatre Trojan comes bundled in spammed messages that imitate emails from known banks such as Lloyds Bank and Wells Fargo. The .MSG file of the malicious emails contains another .MSG file attached with an attached "ZIP" file.
The ZIP files poses as a password-protected archive containing a "secure message" from the intended victim's bank while in reality containing a variant of the Upatre Trojan.
Opening the "ZIP file" on a Windows machine results in an attempt to infect the machine before a download of a variant of the ZeuS (Zbot) banking Trojan ensues. The Trojan then attempts to snaffle online banking passwords.
Other malware is also downloaded as part of the same attack, specifically the Necurs malware, a well-known strain designed to disable computers’ security features before establishing a backdoor on compromised systems.
Upatre can be likened to a sherpa in the world of cybercrime, setting up a base camp for assaults by other cybercrime tools on weakly secured systems. Previous spam runs of Upatre have been associated with the distribution of the infamous Cryptolocker file-encrypting ransomware threat.
Trend Micro has put together a blog post on the evolution of the Upatre Trojan threat - including a more detailed description of the latest "spam within spam" distribution tactic - in a blog post here. ®