One example of such software is a notoriously known XP antivirus, also called Windows XP antivirus 2008. It is a classic rogue software that behaves quite differently from what it claims to do. So, instead of scanning for viruses and removing them, it ruins the system security by opening wide breaches, then installs Trojans and acts like any other spyware – but that's not all. XP antivirus scares the user into buying the full version of it! Of course, the paid version doesn't get any milder on the computer, but it reaches the goal – its creators get money for their evil work.
So how do you tell if your PC has been infected with XP antivirus?
There are signs that cannot go unnoticed:

Windows-like balloons inform about malware detected in the system;
A corrupt Windows security center recommends downloading antivirus software;
Pop-ups scare the user with all kinds of messages urging to get the protection NOW;
While visiting websites you may see annoying pop-ups offering free online scan.

A sad fact about this rogue software is that it stays unnoticed by antivirus programs. To get rid of XP antivirus, you can follow several simple manual steps:

1. unregister DLL-files related to XP antivirus or modified by it;
2. end malicious processes in the Task Manager;
3. remove relevant entries from the Windows registry;
4. locate and delete program files installed by the software.

There's nothing really complicated with the manual removal procedure; any intermediate PC user can do that.
However, if you don't feel like playing with the system and registry (which is always risky), there are tools that can do the removal process for you for free.
Visit the hubpage in my resource box to find detailed instructions on how to get rid of XP antivirus.