What is and why should you have AntiRootkit software

What is a rootkit and how to remove it?

Rootkits are malware that digs into your machine and can be used to hide other virus. There can be many virus that have been hiding under the protection of a rootkit after they were all let in. Sometimes you can't get hold of some virus until you reveal it after removing the rootkit first. Rootkits can be a pain to remove because in order to work properly and not be found easily they really sink their teeth in. This can result in damaging the machine upon removal. So upon attempting a rootkit removal you much know what you are doing as the tools can be very powerful to have to deal with the rootkit.
Kaspersky TDSS Killer
GMER especially is a strong tool and is highly not recommended to use if you are unsure of what to do.