How can I tell if MacKeeper is installed?

I kept getting ads for MacKeeper whenever I visit news sites (particularly ones for my local newspaper). I went to extensions.apple.com and installed the AdBlock software on Safari tonight.

However, when I got a MacKeeper ad before doing so, the ad would not close on the first click. The cursor was a hand instead of an arrow and required me to click on the corner of the ad before I got an arrow and was able to close it as usual.

I'm worried that somehow MacKeeper downloaded on my computer without my approval. I don't want it on my computer, and I'm kind of worried that it could be some trojan/malware/virus type thing (which I really don't need to or want to deal with right now).

Can someone tell me how I can tell if it's on my computer?

And, if it is on my computer, how can I uninstall it?

Thank you!