Chances are it isn't this site, but MSN/Windows Messenger. Do you have Liam as a contact on that? Because I've received a few like that, from Liam and others. What happens is that their Messenger program gets infected by a virus which then sends these spam emails to all their address book contacts.

I use Windows Live Mail to check my emails so often these emails get opened (in a preview window) before I can get a chance to delete them, but the virus is usually transmitted by clicking the link supplied in the email. So don't click on any aspect of the email, just delete it as soon as possible, and block the address so no more emails arrive in your inbox. I know that's probably not much use to you now, but may be useful for others.