A Rootkit is an application that hides its presence or the presence of another software (virus, spyware, etc.) on the computer, by disguising themselves as operating system files which makes them almost undetectable by common anti-malware software. Because rootkits are started before the operating system does, they are tricky to identify and give hackers a great way to access the infected computer without the user's knowledge.
A malicious rootkit provides unauthorized access and administrator priviliges of your computer's system and your data to a remote user. This is done with the intention of covertly stealing user passwords, credit card information, computing resources, or conducting other unauthorized activities. Another undesirable effect of a rootkit is the concealment of malware payloads in a more effective way.
Rootkits can be to blame for recurring virus detections and the best way to remove them is to run the anti-virus scan in Safe Mode. You can find instructions for this in our FAQ section.