A single check standing in for an entire session's legitimacy
Continuous authentication verifies identity on an ongoing, passive basis throughout a session, rather than relying on a single discrete check performed once at login and then trusted implicitly for however long the session happens to continue afterward. Instead of one moment of verification standing in for an entire session's legitimacy, the system keeps gathering signal throughout, watching for anything that suggests the person actually present has changed partway through.
This directly addresses a specific gap ordinary login-time authentication leaves wide open: a session hijacked or taken over partway through — a device left unlocked and unattended, a stolen active session — passes the original login check perfectly well, because that check already happened before the takeover occurred and has nothing left to say about anything that happens afterward.
Passive signal instead of repeated interruption
Behavioral biometrics is one practical way this is actually implemented: verifying identity from patterns in how someone interacts — typing rhythm, mouse movement, touch pressure — rather than interrupting the session repeatedly with explicit re-authentication prompts. The system observes these passive signals in the background and flags a meaningful deviation for further scrutiny, without the legitimate user needing to do anything differently at all to keep the session running normally — the continuous check happens without becoming continuous friction.