Field alert and Cisco Product Security Advisories and Notices (PSIRT) are two popular methods that Cisco uses to announce software caveats, hardware problems, and security vulnerabilities. Both field alerts and PSIRT web pages can be found on the Cisco website (Cisco.com) by using search words field alert and PSIRTs, respectively.
Field alerts are released to the public by Cisco in the hopes of increasing the customers' awareness of potential software/hardware issues. The field alerts typically have detailed information about the nature of the problem and possible workarounds. If there was a bad batch of hardware sold, Cisco typically offers serial number ranges and guidelines on upgrade policy. It is critical for network engineers to be vigilant for field alerts released by Cisco to ensure minimum risk on the production network.
PSRIT is a group within Cisco that is in charge of releasing security vulnerabilities that affect Cisco software/hardware. In recent years, because of sophistication of attacks such as various worms, Code Red and Nachi, it is recommended that you frequent this site.