Recorded evidence of a system intrusion, typically as part of an intrusion detection system (IDS). When a malicious attack is launched against a system, the attack typically leaves evidence of the intrusion in the system’s logs. Each intrusion leaves a kind of footprint behind (e.g., unauthorized software executions, failed logins, misuse of administrative privileges, file and directory access) that administrators can document and use to prevent the same attacks in the future. By keeping tables of intrusion signatures and instructing devices in the IDS to look for the intrusion signatures, a system’s security is strengthened against malicious attacks.
Because each signature is different, it is possible for system administrators to determine by looking at the intrusion signature what the intrusion was, how and when it was perpetrated, and even how skilled the intruder is.