Viruses and forged emails

Symptoms

You are receiving "cannot deliver - no such address" replies to emails you did not send
You are receiving "cannot deliver - email contains virus" replies to emails you did not send
Somebody complains that you sent them a virus

An email from items (1) and (2) may look like:

From:    <postmaster@somedomain.com>
Sent:    Date
To:      you@yourdomain.co.uk
Subject: Delivery Status Notification (Failure)

This is an automatically generated Delivery Status Notification.
Delivery to the following recipients failed:

somebody@somedomain.com

----original message----
From:    <you@yourdomain.co.uk>
To:      somebody@somedomain.com
Subject: something for you
Sent:    Date

ok

The attached file "ranking.zip" was deleted, for reason: Found virus

What is happening?

These are the result of email spread viruses (also known as worms).

Somebody—not necessarily you—gets one of these viruses
This virus emails itself, without the person knowing, to some random person on the Internet, pretending it came from you!

If a virus checker is in place at the recipients ISP, a bounce message (like the one shown above) is sent back to you—not necessarily the person whose computer has the virus.

If the email address does not exist, you will receive a bounce message similar to the one shown above but more likely saying Reason: address does not exist.

The sender email addresses (in this case, yours) are chosen randomly to disguise who actually has the virus and to create as much confusion as possible. Sometimes they are picked up from people's address books or from web sites.

What can you do?

You can mostly ignore these messages. However, make sure your computer has an up-to-date virus checker just in case it really was a virus on your computer that sent the email without you knowing.

If anybody personally complains to you about receiving a virus from you, reply "It is not from me—the address was forged to be mine." Remember to be polite, after all it looks to them like it did come from you!