The industrial espionage of the Concorde project was dected by the French Secret Service and the wing geometry used by the Concorde aircraft was subtly changed. Concorde has no lift augmentation devices such as flaps or slats because the wing design is of a complex nature. It is known as an OG wing, or Optimal Geometry. The aerodynamics of it are far to complex to go into here. The Russians used the spoof data provided to them by their spy and went ahead with construction of the aircraft. The low speed handling of the TU-144 was fairly unstable, and required the addition of small wings which popped out just above the cockpit area when the aircraft slowed to the apporach configuration.
The Paris Airshow crash is now accepted as being caused by the presence of a French Airforce Mirage that was taking photographs of the TU-144. The two aircraft nearly collided, but as the Tu-144 bunted over the top, it exceeded its structural limitations and broke up.
Another reason for the commercial failure of the TU-144 was the very high fuel burn of the engines which reduced the range of the aircraft.
The Tu-144 was used on mail flights within the USSR in 1975 to build up operational data of how to handle the aircraft and was put into passenger service in 1977. Another fatal accident shortly after this was the final nail in the coffin. The last passenger service was in 1978.
In 1995 a TU-144 was reactivated for a series of test flights oprated jointly between the Russian Space agency and NASA. That particular aircraft was subsequently put up for sale on e-bay!