More trouble with Swagbucks search engine (Yahoo)..

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I've been looking up images lately, sometimes for Facebook communications, sometimes for e-cards, sometimes I'm just curious what something looks like--like I wanted to see what a thatched roof looks like. Since Sunday evening, every time I click on "images" for a subject there are nasty pornographic images that pop up. When I looked up "computer malfunction" just a couple minutes ago there was an erotic image. No matter what I put in as a search phrase I get nasty photos in the images. This is something completely new and most unwelcome! I just did a scan and I have no viruses. Any suggestions? Is Yahoo (Swagbucks search engine) infected with a porn virus or is this happening with other search engines as well?