First off these people need to change their passwords for their email accounts, I don't really know what virus it is but this would be the most likely culprit i

First off these people need to change their passwords for their email accounts, I don't really know what virus it is but this would be the most likely culprit is a hacked email account (by bruteforce or maybe a virus as you say). Second of all the only real way, that I can think of, to solve the spam problem (as spammers are perpetually one step ahead) would be a limited web of trust which isn't really a useful way to do email.