When and why did Wikipedia start putting advertisements on its site?

Nothing to worry about, Ofir. All that's happened is that you obviously volunteered your PC, at one time or another, to be an experimental client of Wikipedia's new targeted-advertising campaign in conjunction with the Play Sushi Entertainment Corporation. You've clearly forgotten, but you agreed to let your PC and internet connection "be Wikipedia's and Sushi's *****, for all time, forever, amen". And it seems to be working as planned. You're getting your money, I hope? If not, write in to Wikipedia and remind them. Cheers.