Zeus or Zbot is a Trojan that runs on Microsoft Windows. It was first identified in July of 2007, originally used to steal information from the US Department of Transportation, but didn't start to spread until 2009. It has also, sometimes, installed Cryptolocker.
When it's installed on a host computer, it tries to trick the user into paying for technical support via pop-up ads, and uses Event Viewer to manipulate the user into thinking their computer is infected.
However, in 2010, the creator of Zeus sold the source code to the creator of SpyEye.
Zeus is very difficult to detect with old antivirus programs and other old security software as it hides with powerful stealth techniques. It is considered that this is the primary reason why Zeus trojan has become the most powerful botnet on the Internet. Zeus has infected 3.6 million PCs in the United States in 2009.
However, new and updated antivirus software such as Malwarebytes are able to easily detect and delete Zeus.