Can't get rid of internet files

[jibstar]

I left my mate browsing on the web last night. I went back on here this morning and these files have been downloaded on to my PC bringing up all these porno pop-ups and toolbars I can't get rid of.
They also change the default homepage to http://i-lookup.com/. I found the folders which are responsible for this and I've tried to delete them, but it won't allow me to saying that some files are already in use, even though I haven't got anything running. What can I do?

[aym]

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