Adware on my MAC has recently appeared

I've searched but can't find anything on Malware/Adware for Mac's that helps me.

I have a MacBook Pro (about 4 years old) running OSX Yosemite (10.10.1).

I don't know how this happened but I am receiving pop-ups with several names I didn't ask for or recognize such as (Flashmall, Offers4U, Trovi) to name the one's I recall off hand. I've written the companies when I can find their contact info (not always can I do this) and asked for help... in the end they either do not respond closing the tickets without communicating to me or they provide me instructions that simply do not work.

Can anyone help me get rid of this plague? Since I have a 13" screen you can imagine what it is like to have 20-30 % of it taken up by almost continuous pop ads. Plus it appears to be slowing down my MAC a bit too.

Signed,

Desperate in Las Vegas.