What it is:

RootkitRevealer is an advanced rootkit detection utility.

It runs on Windows NT 4 and higher and its output lists Registry and file system API discrepancies that may indicate the presence of a user-mode or kernel-mode rootkit.

RootkitRevealer successfully detects all persistent rootkits published at www.rootkit.com, including AFX, Vanquish and HackerDefender

Download here.