I've had two in the past three weeks.
One of them created multiple accounts from various AOL accounts. I caught it after they had created 9 accounts over 2 weeks... But no postings yet. I banned the IP. Thankfully they used the same IP for each account.
The second one occurred today. Someone came in and posted using another person's profile. I saw that it was a different IP from the original person. I banned that IP.
And idea how the second one occurred?
Would it be safe to assume that they got in thru the MySQL database?