Most organisations nowadays use a virus scanning system to check e-mail arriving at their site. Some of these scanning systems are set up to send a warning back to the sender address given in the infected message, as a warning that their machine might be infected.
Unfortunately most viruses (and indeed spammers) now forge the sender address. This means that the warning message is sent to entirely the wrong person, causing them confusion and worry.
Properly installed virus scanners for e-mail do not nowadays send back such warnings. Unfortunately some sites are still using misconfigured scanners!
In most cases, as long as you have Sophos (or similar anti-virus software) installed on your machine and regularly updated, such messages can be safely ignored. If you are concerned about such a message, use a search engine such as Google to find out whether that virus fakes its 'sent from' address.
