The Vanguard Terrorist Organization is a secretive underground group who believe that the Federation has become weak through too much diplomacy, they seek to strengthen the Federation by forcing them to adopt aggressive or military positions to fight off enemies that the Vanguard have provoked or the Vanguard themselves, while they are terrorists in the eyes of the Federation, they consider themselves Vigilantes and this makes them extremely dangerous.
Known to use any and every piece of technology that they can get their hands on, the Vanguard is an unpredictable and difficult foe, as evidenced by the USS Vindicator in 240712 when they found themselves investigating the Argos Array which had been modified to tap into the fleet communications network. A small device was found and taken back to the Vindicator, which then suffered a series of malfunctions which ended up in the USS Vindicator losing most of her systems and being towed back into starbase.
The Device, which turned out to be a high-tech hacking node was suspected as the culprit by way of placing a disruption algorithm in the Vindicator's computer system. The crew only managed to neutralize the effects by shutting down, wiping and restarting the computer cores. Subspace weaponry has also been used against Starfleet when they sent a ship investigate an independent starbase, the weapons were high-tech platforms that could fold themselves into a subspace bubble, this made them impossible to detect using conventional methods and could not be targeted or damaged until they returned to normal space to fire.
Some of these weapons also fired Torpedoes that instead of carrying an explosive payload, were meant to breach the hull of a ship and deposit a swarm of mechanical wasp like devices, they each had a phaser as a stinger and some also carried a toxic dart that could incapacitate a Human within minutes.
They have also been known to use Romulan Mind Probes, Dominion based explosives and stolen Starfleet technology as well as work with members of the Mirror Universe. Anyone that encounters the Vanguard should be prepared for anything, they are masters at covert operations and will normally have set traps far in advance of your encounter