But why, when a patch has been available since July 2002, did Slammer hit so hard?
SQL Server is central to many mission-critical systems; running the CRM and ERP applications that a great deal of enterprises depend on. Any upgrades to the SQL Server require time to bring the system down, test it and run it in parallel - time the average IT department simply doesn't have.
Considering the upheaval involved, IT managers would have probably put a patch upgrade of this sort low on their list of priorities.
Seen in this light, the chaos created by Slammer can be considered an inevitable result of IT departments being over-busy and over-burdened. And then you have to give up your Saturdays.