Account activity is the record of actions tied to a user account or session, such as logins, password resets, failed sign-ins, file access, privilege changes, and token use. These logs help defenders determine whether credentials were used by the real owner or by an attacker.
It matters in cyber security because account misuse is a common way to enter a network without triggering obvious malware alerts. During an investigation, analysts compare account activity with normal patterns: impossible travel, new devices, unusual IP addresses, or access at odd hours can indicate compromise. In attacks, threat actors often test stolen passwords, reuse active sessions, or escalate privileges through a hijacked account. In defense, monitoring and correlating account activity with other logs can quickly confirm or rule out suspicious access.