I've recently read an article regarding a distributed denial of service worm is hiding in a new IRC bot called "Voyager Alpha Force", and has been propagating rapidly in the past week. Once activated, systems running the bot search for Microsoft SQL servers running on port 1433, and spread to those with a passwordless system administrator account. Attackers can also trigger the bot to use all infected hosts in a distributed denial of service attack. I recommend that you firewall off this port if possible, and ensure that the 'sa' account is secured with a password.