Most virus scanners can be configured to ignore files of certain types, and there are some files e.g. plain text files which cannot contain viruses so there's no need to scan them...
Thankyou both for your answers. My AV is Bullguard. I am quite happy with it. To check which files it skipped I would have to scan again, this takes approx 30 minutes. you will have gathered I am not very good with either computers or typing.( My hand writing is pretty good though)
I wish we could zxyvixy....My AV is MS Essentials which I have downloaded for free and only hope that it is all it is cracked up to be. I didn't feel like paying £30. to renew full AVG. I know you can have for free a limited edition of AVG ( I've used it) but my experience was that it needed up-dating every week. MSE does scan very quickly and, as I am operating on Windows Vista, I am trusting that it is doing its job efficiently.