The Chechen rebels keep going by generating cash from criminal enterprises Chechen gangs have specialized in since the World War II. The money allows rebels to bribe Russian soldiers, but Russian weapons and, apparently, have Russian  portable anti-aircraft missiles modified so they will hit Russian aircraft. These missiles have a device in the warhead that makes the missile swerve if it encounters an aircraft broadcasting Russian IFF (Identify, Friend or Foe) signals. This system was always considered of dubious usefulness, because of technical and problems.