Ok, my sis is getting TONS of windows that look like yahoo instant messanger IMs, but they are from "SYSTEM", and they say she needs an update of her IMer, they are not actual IMs, because where there is usually a box to type in a response is cut off, and there will be 20-30 of them when she gets up in the morning, all saying the same thing.

There is a link to click on them, but I told her that until she knows what they are, she shouldn't click on them. She has run her virus protection program and disc clean up and defragged... OH! and she already has a popup blocker and it IS turned on, she NEVER gets popup adds... just this new peculiarity.

What are these things and how do you stop them???

She has window XP and cable internet.

Welcome to the THF. I would suggest you read the notes here http://www.techhelpforum.com/forumdisplay.php?f=32 then run Hijack this and post a log for the experts to take a look at.