If you are lucky, your friends won't send you a virus. But if a friend does send you a virus, what will you do?
More than likely the email address of your friend was spoofed. This means that someone decides to make a double dose of trouble by sending out a virus laden email and make it look like someone else sent it. (This can also happen with SPAM.)
However the email may have come from your friend's computer, but was sent without the friend's knowledge. This happens when a computer becomes a zombie computer and part of a 'botnet'.
The best thing to do if your friend sends you a virus is look carefully at the email. Does it have a subject? Usually not, but some of these malware writers are getting better at what they do, so this may not apply.
Is there a message or just a link? Again, this is an indication of malware, but can't be taken for granted.
The plan of action here is to reply to the email and ask your friend
what this is about? If the email was sent by your friend they will most
likely reply and tell you what 'it's about'. But if the email was sent
without your friend's knowledge, then this will be an alert to let them know
their computer is infected and to clean it of the infection.