It is considered that this is the primary reason why the Zeus malware has become the largest botnet on the Internet: Damballa estimated that the malware infected 3.6 million PCs in the U.S. Zeus is very difficult to detect even with up-to-date antivirus and other security software as it hides itself using stealth techniques. The scammers may use programs such as Command prompt or Event viewer to make the user believe that their computer is infected. Similarly to Koobface, Zeus has also been used to trick victims of technical support scams into giving the scam artists money through pop-up messages that claim the user has a virus, when in reality they might have no viruses at all. In June 2009 security company Prevx discovered that Zeus had compromised over 74,000 FTP accounts on websites of such companies as the Bank of America, NASA,, ABC, Oracle,, Cisco, Amazon, and BusinessWeek. First identified in July 2007 when it was used to steal information from the United States Department of Transportation, it became more widespread in March 2009. Zeus is spread mainly through drive-by downloads and phishing schemes. It is also used to install the CryptoLocker ransomware.

While it can be used to carry out many malicious and criminal tasks, it is often used to steal banking information by man-in-the-browser keystroke logging and form grabbing. Zeus, ZeuS, or Zbot is a Trojan horse malware package that runs on versions of Microsoft Windows.

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