This is the timestamp of the last time the gateway checked for a new Anti-Virus signature update, regardless of whether an update was actually found. This tells the admin whether the update-checking process itself is still running on schedule, which is distinct from whether an update was applied: a recent check time paired with an old signature date would mean updates are being checked for but not successfully downloaded. For example, a check time from five minutes ago paired with a two-week-old signature date would point to a download failure rather than a scheduling problem.