I've completed an analysis of the 'Sapphire' SQL worm targeting MS-SQL servers. Some have reported massive slowdowns. An interesting part of this worm results from its use of UDP. Attacked hosts/networks may generate ICMP Host/Port Unreachable messages in response to a Sapphire attack, amplifying the attack's strength. One reason that this attack is worse for users of home systems, etc. that don't run any servers, is because Sapphire sends the entire 400 bytes or so in the initial packet, where scans from Code Red and bretheren only prompted a 26 byte TCP SYN packet. The full analysis is available at: http://www.techie.hopto.org/sqlworm.html
