What are rootkits?
It’s a technique used by software to gain long-term access to a computer without having the required permission. Rootkits are typically installed by other malware to cover their traces. For example, a keylogger might siphon off passwords and credit card details, while the rootkit hides the traffic to keep the theft unbeknown to the user. Other cases involve Trojans that install a rootkit in order to create a botnet.
Companies such as Sony have been known to use rootkits to track the spread of CDs online.
How to block rootkits
Most antivirus software detects and blocks rootkits. You can learn more about and download Avira Free Antivirus here.