Keylog/PerfLogger.ZI is classified as a Keylogger.
Keyloggers are applications that log keyboard and/or mouse input.
The Fortinet Anti-Spyware Research Team is currently in the process of creating a detailed description for this Spyware.
For additional information about Keyloggers, and how Fortinet classifies Spyware threats please see Fortinet's paper in PDF format:
Spyware Classification and Terms.