No, not a bomber, it is supposedly a spy plane.
Another reason why I don't think it exists is that its capabilities are no longer what is required of a reconnaissance aircraft. Due to the nature of current conflicts, a plane that that watch an area of a long period of time is much more valuable to us than a plane that can take a few photos and leave (possible one reason that the -71 was retired). Because of this, UAVs like the Predator and Global Hawk were developed because they can sit over a target for 12-24 hours continuously taking and transmitting real-time video... and they don't get tired.
Also, I find it highly unlikey that any manned aircraft could hit Mach 6, or anything even remotely close. The X-43 hit approximately Mach 10, but that was basically an engine with wings. I think it is impossible with current technology to achieve Mach 10 with an aircraft of significant size.
Another reason the SR-71/ A-12 was retired was due to increasing numbers of spy satilites that could do many times more work.
Maybe we are being mislead to think it is a spy plane, maybe its just a cover story for a new long range, high speed, high altitude, bomber???
Then again, it may just be a hoax...