Source: Star Trek the Next Generation
Location: All over the universe
Threat Assessment: 8. They are a hive mind that will take victims and turn them into more Borg. Borg are strong, nearly invulnerable and armed with energy weapons. Their square ships are also nearly invulnerable.
Limitation: They lack style. They tend to do things on their own time, sometimes stopping a battle to repair or do other functions giving their foes a needed breather.