Verified answer

I found a website about malware removal that said to change your email password. Searching Google turns up a lot of people having this problem. Also the emails have a blank subject line.

That is because it is a malicious site. It will run a script that tells logged in webmail to send spam to the address book. That sets of a web of people who know each other and are in each other's address book receiving the spam, clicking the link, and spamming each other with it.