How is it possible that I am sending viruses when I haven't been sending email?
The most recent email viruses and worms (which are a different classification of virus) attempt to burrow into your system unnoticed. Once your device is infected, viruses send themselves out as fast as possible to as many systems as possible. They do this by looking at various sources of email addresses on your system, such as your address book or even your sent mail and mail cache. By using this method, they can more easily appear to be a legitimate email because they can send to people you've emailed before or who have emailed you.
To complicate matters further, many of these viruses 'queue up' a series of infected e-mails to send out even if you're offline. The moment you connect, they immediately begin spewing forth in an effort to infect more unprotected systems. Some more devious viruses even contain their own mail propagation mechanism, where they can appear as a mail server trying to make a connection to another mail server. Situations like this can make it more difficult to track the sender. Rose-Hulman uses