Variants of the Zeus Trojan were the most distributed pieces of malware, by spam, in August 2013, researchers said.
The Zeus malware was in 23 percent of all the malicious attachments found in spam emails. After Zeus, there is Fareit (19 percent), Mytob (9 percent), Tepper (8 percent) and Wauchos (7 percent), according to the Trend Micro report.
The spam notifications used to distribute Zeus and Fareit stand out because they replicate legitimate messages that appear to come from well-known companies, the researchers said.
After installation on a computer, Zeus waits for the victim to visit certain banking websites. When the user visits that site, a malicious page ends up injected in an effort to trick the user into handing over sensitive personal and financial information.
Fareit, on the other hand, steals email and FTP login credentials. It’s also capable of downloading other threats onto the infected device.