The scarce information available about The Five suggests that ComStar, during the reigns of Jerome Blake and Conrad Toyama, used its control of communications and mapping to deliberately hide the existence of worlds that had been depopulated and devastated during the maelstrom of the early Succession Wars, maintaining them in secret as havens, manufacturing and fallback sites for the Order. The process of hiding these worlds was achieved through retro-active alteration of star maps throughout the Inner Sphere and shell games involving name changes.
Besides The Five, numerous other hidden worlds exist; some were lost colonies (re-)discovered by the ComStar Explorer Corps (such as Alfirk or Haddings), others (such as Roxborough) were settled by the order. Some, like the Luyten 68-28 facility, had previously been secret military facilities of the collapsed Star League that fell under ComStar control.
Information indicating the existence of the The Blood, a rumored cabal of Clan Wolverine descendants hidden within the ComStar organisation, refers to The Five falling under the control of The Blood during the reign of Raymond Karpov. The existence of The Five was known only to very few high-ranking ComStar officials; Myndo Waterly was the last Primus privy to that knowledge. Intending to use the resources of the Five to reinforce her public forces in the wake of Operation Scorpion, seeing little chance of success the "Master" refused to aid her. After Waterly's death and the organisation's schism, the knowledge and control of these worlds resided solely with the Master and the Word of Blake, the remaining secular ComStar order almost entirely unaware of their existence. 
At some point, possibly from the onset, The Five were centers of weapons research and construction, thought to be created as secret fortress worlds from which to wage war on the Clans. They have been revealed to include a large shipyard, a bioweapon research center, and a cybertech center. The mysterious Manei Domini and their Shadow Divisions were rumored to have originated from the Five.
The Five were reportedly defended by descendants of the Clinton's Cutthroats mercenary unit, hired in secret by Karpov after the accidental discovery of one of the worlds on 15 October 2869 and permanently settled on The Five.
Jump data for supply runs and contact with the hidden worlds was a closely guarded secret, hidden in plain sight and embedded deep into the firmware of the HPG network. During the pre-Schism era, those few trusted with knowledge of the Five were issued a special noteputer to connect to a HPG and access the required security protocols. After providing three separate passwords, the HPG transmitted a self-purging course to the appropriate Hidden World to the attendant JumpShip. 
Once the Five fell under the sole control of the Master and the Manei Domini, the Word of Blake made extensive improvements to these security protocols, integrating it into the cybernetic implants of those Domini with appropriate clearance. Expanding off the Manei Domini's ability to direct link to BattleMechs, three separate high-ranked Manus would simultaneously remote-access a HPG and think their way through the security protocol, their implants reading the information and transmitting the decryption key to the HPG, again transmitting a self-purging course to the intended Hidden World. 
One hidden world supposedly lay in the territory of each of the five Successor States, though it is possible that the one associated with the Capellan Confederation ended up in conquered territory following the Fourth Succession War. One report indicated that one world, most likely the one in the Draconis Combine, was dead even before the Jihad began.
The known worlds are
- The Ruins of Gabriel (Lyran Commonwealth space) turned out to be a shipyard complex hidden in the Lyran system of Odessa. Gabriel was found and attacked by a coalition battle fleet.
- Jardine (Free Worlds League space), previously also known as Herakleion. Apparently a center for cybernetics and presumably the homeworld of Precentor Apollyon and the Manei Domini. Thomas Marik was brought here to be treated for the injuries sustained in the bombing that killed his father. His double (Thomas Halas) was trained on Jardine. Brooklyn Stevens found Jardine during the Jihad, but her team was hunted down and terminated. Later, an expedition sent by Thomas Halas found that the planet Jardine had succumbed to a natural disaster known as a traps volcano, and had become totally uninhabitable.
- Mayadi (thought to lie in Draconis Combine space and speculated to have been depopulated by a bioweapon breakout, in turn speculated to have been caused by bioweapons research conducted there)
- Taussen (thought to lie in Federated Suns space)
- Obeedah (thought to lie in Capellan Confederation space)
While the existence of the Five is Canon, significant portions of the background about them originates from unreliable in-character testimony and from so-called Canon Rumor sources which complicates and clouds their true history, at least until later sources are released to corroborate or dispute them.
- The Blake Documents, pp. 127-128 "The Not-Named"
- Jihad: Final Reckoning, pp. 129-131 "Legacies of the Word - The Hidden Five
- The Blake Documents, p. 114 "Karpov's Leagcy"