This counts identified sessions currently protected by the anti-spoofing check, which verifies that traffic actually originates from the IP address associated with that user's identification. This defends specifically against session or IP hijacking, where an attacker tries to reuse an already-authenticated user's IP address to inherit their access rights, so this count shows how many active sessions carry that extra verification. For example, 300 out of 342 authenticated sessions might have anti-spoofing protection active.