You’re not alone. People with malicious intentions are scanning for open SIP servers all the time. Aster1sk from Geekhut.org posted a useful video for those of you using a badly configured FreePBX + Asterisk. I’m sure this will be useful for someone..

Sandro Gauci, Enable Security
Getting phonecalls during the middle of the night on your Asterisk server?
Published on Dec 10, 2009 in asterisk, sip security