Swarmers are known to be the only microships equipped with any kind of weaponry - it's light Mass Driver wasn't very harmful alone, but could be deadly to any kind of strike craft when there were several Swarmers using them. Each ship also contained it's own sensors, efficient drive and AI.
The concept of these drones came from the Kadeshi Swarmer [proof of basis needed], a very light fighter with no known form of sensors (it is assumed that their craft were visually piloted), and only a dual-barrel weapon mount. It was adapted to the concept of a controlling Frigate, and that ship got an advanced AI control system for both combat and movement. Thanks to this, the Attack Drone could maneuver between enemy units delivering it's firepower straight into enemy fighters. Such systems also saved space onboard Hive Frigates, which was critical when it came to mounting Frigate weaponry.
These Attack Drones were proven to be very efficient in combat against strike crafts, yet even a group of a dozen or so of them wasn't a real threat to enemy capital ships. What its greatest advantage was during combat with agile units became the source of it's greatest flaw - the Swarmer lacked weapons heavy enough to pierce through capital-class armor plating or their reinforced hull structures. Therefore, Swarmers could try to attack Qwaar-Jet-class Heavy Cruisers only in numbers of several squadrons (fruitlessly), and still they were only useful as support for a real strike force.