The Swarm

Voyager tries to cut through the territory of an aggressive, little-known species whose ships attack in swarms, after Paris and Torres are attacked on a shuttle near its border. Once Voyager enters the region the swarm ships latch on to the hull, and Harry Kim discovers that they are linked in a lattice that collapses when a single ship is destroyed.
Meanwhile the Doctor's program is breaking down because he has expanded far beyond his original design. Kes and Torres call up a holographic diagnostic program modeled on his creator, Dr. Lewis Zimmerman, which concludes that a full reset would wipe out everything the Doctor has learned. In the end the diagnostic program merges its matrices with his to save him, and the Doctor survives, though with gaps in his memory.