It is not a virus. It is malicious code from a third party gadget you have on your blog. Best thing is to remove any third party gadgets you have added to your blog in the last few months one at a time until the problem goes away...this way you can narrow down the one that is causing the problem.
If you can't remove them using the layout page, we suggest editing them out of the template html but you will need to back up your template before attempting this just to be safe.
Mishka
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