you may want to see who else has access to it. Generally (unless something is downloaded via share, like edonkey and what not) the porn ads are due to visits to adult sites and "free" sample vids are downloaded which in turn install these objects. The other things that cause this are the above, use of things like edonkey, old kazaa, bit torrents, etc. The script is contained in the actual file (header???) and it puts this ad in there. I'd say, maybe neighborhood kids or something may of gotten on it (happened to my folks, turns out next door neighbor little 12 year old turd was showing my nephew, on my nephews request, some funny and adult stuff). Long story short, tell them to make sure to keep a close eye on who uses it.
If you argue with an idiot he will drag you down to his level and beat you with experience.
I am not a fast writer.
I am not a slow writer.
I am a half-fast writer.