Some program I downloaded a couple years ago had one of these on it, and I didn't see it when installing.
It installed AskJeeves on my computer, and since then I've had it stuck on my computer.
It acts as my default search engine (although it's terrible), and used to sporadically change my home page to Ask.com
Luckily it seems to have stopped being so annoying, and I can generally ignore it being there since it doesn't come up much.
But when I previously tried to uninstall it, from my browsers and computer, it wouldn't let me uninstall due to random programs using it, or needing permissions (despite my user profile being the only one, and being administrator).
I could probably delete it now, but I can't be bothered too. Has been a pain in the arse before though.