This plugin used to scan the content directory as well as the database for any kind of threat.
It searches PHP files for the occurrence of the eval() function, which, although a valuable part of PHP is also the door that hackers use in order to infect systems. The eval() function is avoided by many programmers unless there is a real need.
It is sometimes used by hackers to hide their malicious code or to inject future threats into infected systems. If you find a theme or a plugin that uses the eval() function it is safer to delete it and ask the author to provide a new version that does not use this function.
A clean scan does not mean you are safe. Please do Backups and keep your installation up to date!
Requires WordPress Version: 2.6 or higher