Heed NAC's warning, paracab! This is FAR from trivial!
You DO have an updated anti-virus programme running, don't you.....?
AS NAC says, if you do not know the nature of the att., better not to try to open it until you do.
PS. If it comes from an unsolicited source, do not email the source back asking for more info, as this validates your address to a potential spammer. If it comes (apparently!!) from a 'friend', beware if you are not expecting it.
In that situation, I always click on the attatchment, select 'save to disk', and run it through my virus checker BEFORE opening. You'd be surprised at what viruses some of the attachments carry!! I am not aware of any virus that can execute simply on a 'save', but am willing to be corrected there (and to change my procedures!
)