They install malware (Not just toolbars the impossible to remove without a reinstall variety).
Never came across those ... I do have kids using a PC installing all types of toolbars on a weekly basis. Do, do you mind to name the toolbars in question ? Will install it tonight as soon as I get home and will post instructions tomorrow on how to remove.
I had removed one homepage-hijacking thingy that was very well installed ... it added itself into the
"Command\Open" keys, such as Hkey_Local_Machine\Software\Classes\html\Command\Open and the equivalent for firefox, chrome, ie programs (do not have windows at hand, cannot check full path, sorry). Appended itself into all browser shortcuts across the system, as well.
Been removing viri from Windows boxen since 2000. Have not yet come across a virus for Mac/Linux, though I have heard myths.
I recently also wrote a little tool to find root kits ... pretty simple, actually ... full drive listing from cmd.exe's dir and the same from VBS, then diff the two - cmd.exe will list some dirs that VBS does not - those are the root kits ... ;-) If you are computer savvy, you can do the same from a linux livecd, diff the lot and sort.
Of course, you need to know the NTFS file system, windows directory hierarchy etc to be able to find suspects ...
I occasionally give tramps a coin - I have a heart for the deprived.