FIrst off my small woot for 200th post. Wanted it to be a tutorial but it still needs work before i post it and this can't wait.

So my fiance's mom is still on dial up and recieved a surprise on her phone bill this month. Some type of phone long distence phone call was made to russia on her comp. this raked up a nice 60 some odd dollar bill.
Being the techno person joining there family circle i'm kinda being accused for it being something i did or downloaded on there comp. I'm pretty sure this isn't the case because from besides installing Firefox, ad-aware, and spybot search and destroy i havn't done to much besides read this forums on her comp.
So i'm trying to figure this out and i can't come up with the proper google search for this so I'm turning to the masters.
My two ideas are either some type of of porn site (not me either) or some type of hack.
Can someone please help me out on this one and let me know what they think I'm don't wanna look bad in the eyes of the person I'm going to call mom in the future.