Resolved - Help! please - if you can. I Think I Have Malware on My Computer

Over the last week or so I have when visiting my usual websites and forums etc. been seeing these buttons which simply say "Play Now" and "Download" (screen shot attached).
There is no other text with them and of course there is always temptation to click on them. I never have and really thought nothing more of them until today, when an affiliate manager contacted me with a new rotating banner ad. which I placed on one of my sites.

Having placed the banner code in the appropriate place, I viewed my site to make sure it was working and to my surprise, the rotating banner shows a legitimate ad on the first one and then the self same buttons i have been seeing elsewhere. The ads then no longer rotate.but remain showing these buttons.

At first i thought an infected code, but then realized it may simply be on my computer. I use firefox mainly and looked at my site using g. chrome and do not see the offending banner then. So I deleted f/fox and installed a completely new one but am still seeing these dam buttons. I have of course taken them off my site by deleting the code (which is iframe by the way) until I can find a solution.

I am still seeing these buttons on other sites .!!

Has anyone else had this experience? if so how the hell did you overcome it?

Please help if you can ....many thanks in advance