Among other things, this means that if you didn’t get spammed by me, then you are not in that particlar contacts list. But more importantly, this kind of thing can happen to anyone, so watch out. Fortunately, I knew immediately that something had happened. How? Two ways.
First, by keeping a couple of obsolete and invalid addresses in my contact list. The mailer-daemon (or whatever your system calls it) sent me a message for each one telling me that the email which I knew I never sent was undeliverable.
Second, I have multiple email addresses, and each of them has at least one of the others in it’s contact list. I have my reasons. Among others, I was able to view the spam that I sent to all my contacts.
Either of these methods, assuming you check your email regularly (read: obsessively), will let you know that you’ve been hit by a spambot. Change your password and scan your computer right away so it doesn’t happen again.
This has been a public service announcement from the Mister Pterodactyl Consortium. Eternal Vigilance!