There's now a threat to online life that's so potentially potent it requires a new form of defence. Rootkits hide inside the operating system, actively defending themselves and hiding their presence. To arm your system against rootkits, you first need to understand them. So, where have they come from, how have they evolved and how, crucially, can they be stopped?
A rootkit is a program that allows a hacker to come and go as he pleases, unhindered by your computer's defences. No firewall will stop him and no antivirus program will detect his activities. Rootkits subvert the way the operating system works to make it lie about the processes, files, Registry entries and kernel modules that might give away the rootkit's presence to humans and antivirus software.

Unlike viruses, rootkits have had a low profile for the past 20 years, but that's changing as their methods merge with those of mainstream malware to produce a threat that requires dedicated software to deal with it.

The name 'rootkit' comes from the 'superuser' account in Unix (and Linux). This is called 'root', and logging into it gives the user complete control over the computer, arguably even more so than an administrator account does in Windows. Normally, only a system administrator has access to root because it's so powerful.

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