Nanochip

Nanochips (aka Microchips or Nanites) are objects used by the hive.

Biology/History
The Queen produces them from her body and later after she takes up residence in Victor Validus' body, she produces them from there and they have the ability to take over a person's mind. They are a hybrid which is part organic matter and part machine as pointed out by Kevin. The Queen was destroyed by Ben in the form of Nanomech.

The nanochips surprisingly returned in the Ben 10: Ultimate Alien episode Revenge of the Swarm. The team discovered that the chips took over Elena Validus' mind and had made her the Queen of the Hive. After Elena sacrificed herself for Ben by destroying her nano self, the chips still had some life in them.

Omnitrix Transformation
The Omnitrix's Nanochip representative is named Nanomech, who first appeared in the film Ben 10: Alien Swarm after the recalibrated Omnitrix scanned several nanochip-possessed humans. Nanomech has appeared in almost every subsequent series except the reboot.

The Ben Tennyson of Dimension 23 has an equivalent of Nanomech named Teeny-Weeny, who was confirmed to exist in the Omniverse episode "It's a Mad, Mad, Mad Ben World: Part 2".

Nanomech has also been used by the Prime Timeline Kevin.