'Some' spammed files appear as normal files but are not, may be linked to porn files. Perhaps your friend was downloading porn files, or just choosing wrong ones & they hyper-linked him to various sites via the browser. Need to learn which file sizes to avoid: Virus thread: Typical virus spam file sizes - Make a note of them (click on blue link to see).

Secondly, you can filter out some types of searches: Direct instructions to eliminate porn from results (the links within this post have important words to filter out via your keyword filter.)

This way, LW cannot be used as a scapegoat at least.