my ma-in-law's HTC has been doing the multiple re-sending of SMS/MMS messages thing, and I was wondering whether it's a virus or something to do with the phone or something to do with the network.

Any clues?

Googling for info on HTC viruses only brings up form posts, etc. from late last year and nothing recent. Can anyone recommend a good, trustworthy (preferably free) anti-virus app? Does such a thing exist? Or is the whole situation a product of my delusional mind?