Download the tool from www.f-secure.com and run it (No installation required). It will do a quick check for rootkit symptoms and proceed with scanning and removing infections.
You may want to disable your anti-virus program before running F-Secure Easy Clean, because they may block access to some files, so F-Secure Easy Clean cannot scan or clean them. Turn on your anti-virus program after finishing the scan.
Remember that it is not a full antivirus product. It does not remove all the known malware; it focuses just to the most common viruses, worms and other types of malware in the wild.