BOS Controller described ASDE-X anomaly when the target of an aircraft on final veered left toward traffic holding in position and then disappeared; reporter claiming ASDE-x is unsafe and should not be used until it can be verified as reliable.

Narrative

I was training on LCW in IFR ASDE conditions (vis 3/4 ra br). Aircraft X cleared to land on Runway 4R. Traffic was holding in position on both Runway 9 and Runway 4L awaiting the arrival of Aircraft X. Aircraft X appeared on ASDE-X at approximately 1/4nm final...then target and aircraft symbol veered left as if turning towards Runway 4L...when target on ASDE-X was over Mike and Bravo Taxiway; the entire target (1 bit video and aircraft symbol) DISAPPEARED!!!! GONE!!! NOTHING!!! I had no idea where he was!!! I immediately overrode my developmental (who also saw the target turn and disappear) and issued GO AROUND instructions to Aircraft X...of which he complied. This is just a continuation of mishaps with the ASDE-X. This system has been reported on from inception as being unreliable; inaccurate; and completely unsafe. Nobody wants to listen. I had NO IDEA where this aircraft was...my anxiety multiplied tenfold by the fact that his last heading on this 'digitized radar' system was directly towards a large group of aircraft on the ground. Recommendation; my honest recommendation is to REMOVE the ASDE-X system and reinstall the old ASDE-3. The ASDE-3 RADAR was raw; real radar...super reliable...phenomenal picture quality AND completely TRUSTWORTHY! This ASDE-X system is going to cause a horrific accident....it's just a matter of WHEN? This is completely UNSAFE. It has been since I first saw it installed at another facility. Management refused to listen to any criticism then and accepted the system against major concerns from controllers. Now BOS management is doing the same thing. It's only a matter of time. STOP using ASDE-X until it works like it is suppose to work!!!