adSense trojon - How to remove (please help)

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My computer got infected by a trojan.

Basically it replaces Google or YPN ads with some other ads.

used different options to remove the virus but it did not work.

http://www.dnforum.com/f467/ypn-shoing-image-ads-just-saw-them-thread-318504.html

It happened and initially I thought YPN start serving image ads, they are showing on my sites.

Then I found out that it happens on adSense ads and YPN ads only on one of my computers.

Any clues on how to remove this trojan.

Thanks