At about 9am yesterday morning, I noticed on the monitor that the CPU utilization of one of my servers was abnormally high, in addition to a sustained 1mbit/sec of inbound traffic and 2mbits/sec of outbound traffic. syslog messages from Asterisk showed it to be a SIP brute force attack, so i dropped the offending IP (an Amazon EC2 instance IP) into /etc/idiots to block it and went back to my work.