I hate to call 'viruses' and those who creat them 'smart', but they have gotten more clever.

What they seem to do is grab someone's email name and address from another person's computer and then send out virus laced emails from yet a third person's computer.

This makes it look like the email is coming from someone's PC (like Bert's) when it is not.

Safest bet is to always use protection that checks in-coming and out-going emails.