Most viruses and worms are spread by email, in the form of spam (or junk emails). So how are these emails sent?
Viruses/worms install their own SMTP engine on compromised computer, once installed; a worm can churn out a huge volume of messages on a broadband connected PC by sending mail directly out of port 25 rather than the Optus mail server. By blocking port 25, such viruses/worms can be stopped from spreading, and has the added benefit of reducing the amount of spam that is received in all Optus customer’s inboxes.
