This is the number of times a specific virus in the current top-viruses table was detected and blocked during the current reporting period. A sudden large jump in this count for one named virus, versus a steady background rate, is what distinguishes an active outbreak attempt from routine day-to-day noise, and is the number admins would cite when justifying isolating a suspected source host. For example, a hit count jumping from 3 to 300 in an hour for the same named virus would justify an immediate investigation into which host keeps triggering it.