A rootkit is a program designed to enable unauthorised, remote administrator access to a computer by opening a backdoor. Rootkits don’t replicate themselves like worms and viruses do and are usually installed through phishing scams, executable files, or software downloaded from a dodgy website. Once installed, an attacker can connect to the infected machine and introduce other malware to steal information. Rootkits usually hide themselves on the infected machine and can be difficult to detect.