There might be some long-idle lurkers who read this only after discovering their accounts have been deleted.
The problem is, over the last couple of weeks, and especially the last couple of days, there have been a flood of spambots that somehow got past the Q&A registry question and began posting spam posts. As part of the countermeasures we're taking, all accounts with zero posts have been deleted.
All of them.
This doesn't necessarily mean anything bad. It just means we've had to nuke some legit accounts in order to purge a raft of spambot accounts.
So, if you just found out your account was deleted, re-register- and then POST SOMETHING.