Upfront preparation helped my company ward off the SQL Slammer worm, which exploits a buffer overflow vulnerability in Microsoft SQL Server and creates a flood of packets, similar to a denial-of-service attack. But we still didn't totally avoid it.

Shortly after the worm appeared, we decided to run scans of our infrastructure to find and patch vulnerable systems. In the interim, we implemented Cisco Systems Inc.'s Network-Based Application Recognition (NBAR) feature on our core edge routers, configuring it to drop any packets that matched the signature of the SQL Slammer attack. The problem with NBAR is that routers are designed to route traffic, not inspect packet payloads. NBAR consumes a considerable amount of router resources and can lead to performance problems, so we didn't want to keep it in place any longer than necessary.

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