I also went through and pruned a lot of old accounts that have never been active, some of which may have been spammer sleeper accounts. When the board was upgraded last week for some reason it disabled the security question and a horde of spammers registered within minutes. I thought I got rid of them all, but some probably slipped through, only to activate a week later.
Sorry about the spam today

Hopefully we'll now return to normal spam levels, which are usually pretty light!
Also, thanks to everyone reporting spam posts and I'm sorry if I don't PM you to thank you directly. I often delete the posts en masse, and any reports associated with them get erased before I check them.