It seems like about twice a month that I receive an email from a friend or client with nothing but a link to a .cz, .ru or other questionable site. So far, every one of these has been a mass email from their account (sent to all their contacts) after their account password has been compromised. My guess is that some malware takes hold in the machine, captures their password the next time they log in to (usually Yahoo) email, and uses an API after that to send out spam with the newly-acquired credentials. Here's my standard response:Hi <insert-name-here>;It looks like your email account has been compromised...your account sent this link (to a questionable web site) to a large group of your contacts.You should change your email password, and run an antivirus and anti-spyware program....I like http://malwarebytes.org for spyware removal. There are simple instructions for running Malwarebytes here: http://gary.stanley.net/malwarebytes.htmLet me know if you need help!John