Friend Claims You Sent a Virus

Most likely there is no virus on your computer, sending phantom emails. If your virus protection is up to date, the more likely situation is that a third party you both know has a virus, and the emails are coming from that person.

It's quite common for viruses to send rogue emails, randomly inserting an entry from the address book into the From: and To: tags of the outgoing messages. This is how they often spread, on the hope that the victim will open the attachment because it comes from a person known to them.

Bottom line: If someone has your email address in his/her address book, and they have a virus, it may appear that YOU are sending the virus-laden emails. A careful inspection of the email headers (in particular the Received lines) can shed more light on where an email originated.