Zeus (also known as Zbot, PRG, Wsnpoem, Gorhax and Kneber) is a Trojan horse that steals banking information by keystroke logging and Form Grabbing. Zeus is spread mainly through drive-by downloads and phishing schemes. Zeus is very difficult to detect even with up-to-date antivirus software. This is the primary reason why its malware family is considered the largest botnet on the internet: Some 3.6 million PCs are said to be infected in the U.S. alone. Security experts are advising that businesses continue to offer training to users to prevent them from clicking hostile or suspicious links in emails or on the web while also keeping up with antivirus updates. Symantec claims its Symantec Browser Protection can prevent "some infection attempts", but it remains unclear if modern antivirus software is effective at preventing all of its variants from taking root.

The Zeus botnet is targeting login credentials for online social networks, e-mail accounts and online financial services. The top sites with stolen login credentials, according to Netwitness' report are Facebook, Yahoo, Hi5, Metroflog, Sonico and Netlog. While the focus has been on e-mail and social networks, Kneber is now targeting banking sites as well.

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