The PushDo trojan has been around for a while, but recent variants are making it more difficult for security researchers.
PushDo infects vulnerable computers when users visit an infected web site (drive-by download). Once installed on a computer, PushDo sends out phishing email purporting to be from banking institutions, tricking other users into clicking links within the email and infecting their computers with other malware.
What makes the new versions of PushDo different is that they hide communication with the botnet’s controlling servers amongst a flurry of traffic to other, unrelated servers. This makes the process of finding the controlling servers much more difficult and time-consuming.