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I was working Local East and had a CRJ cleared to land on Runway 26. Right before the aircraft touched down on the runway; the ASDE-X alarm went off and said to 'GO Around Runway 26'. I saw a couple of targets on the taxiways holding short of Runway 26 but I did not see anything on the actual runway. As required; I instructed the CRJ to Go Around and gave him further instructions. I received no response from the aircraft and so I again instructed the aircraft to Go Around 'if able'. This time the aircraft responded and went around. I am not sure why the system alarm on the ASDE-X went off; but it was determined that there was not a vehicle on the runway. It may have been a reflection or a false target response. Either way; the aircraft was literally about to touch down on the runway and was in a critical phase of flight. Sending the aircraft around at this point in time may have been more unsafe then letting him land but as required by the ASDE-X; I have to send aircraft around when the alarm indicates to do so. I would just recommend further investigation on the ASDE-X and false targets. Maybe we can figure out what causes this to happen in order to prevent it from occurring again.
A PHL Controller issued a very late go around in response to an ASDE-X Alarm. The reporter noted the go around may have been unsafe and not needed but mandated by ATC rules.