Fun fact, Rush from the anime is based off of viruses called Moles in the games (in the English version of the games at least, they're actually still called Rush in the originals :P ). The battle chip you can get from them is called PopUp, which made me think that they probably act like pop-up ads. :XD:

As advanced as the Battle Network world is, they still have viruses to deal with, so they probably have plenty of other computer-related issues too (pop-up ads, spyware, lag, etc).