GDS - Major Data Source for ALL Intelligence and National Police Services
The data retained by GDS is accessible, without warrant or other impediments, by all major intelligence agencies and the larger, or national, police entities.
Many Third Party Res systems run by some notorious on-line travel agents' also have unlimited access. too. This includes several in the USA and a couple in the UK.
Unbelievably, when the GDS (read > https://en.wikipedia.org/wiki/Global_Distribution_System <) were developed by the airlines, there were few checks - everything was based upon 'trust'. After all, these systems were subsets of airlines.
Then they started interconnecting and do bookings for Third Parties and ticketing commission was viewed as potential compensation for the costs of running these systems. To avoid claims of conflict-of-interest the systems were hived off from the carriers but still based on 'gentleman's agreements'.
Gentlemen's agreements are defined in Wikipedia as: "A gentlemen's agreement or gentleman's agreement is an informal and legally non-binding agreement between two or more parties. It is typically oral, though it may be written, or simply understood as part of an unspoken agreement by convention or through mutually beneficial etiquette. The essence of a gentlemen's agreement is that it relies upon the honor of the parties for its fulfillment, rather than being in any way enforceable. It is, therefore, distinct from a legal agreement or contract, which can be enforced if necessary.'
In fact, the airlines/carriers relied upon these former carrier entities to do their ticket accounting!
The GDS/CRS systems used to deduct their 'cut', aka commission, from the money they paid to the airlines. From this 'cut' they would pay commissions to user travel agents.
When the airline business was stressed, the airlines started to use software to ensure that the GDS/CRS commissions were credited when tickets and - surprise, surprise - the airlines discovered they were being bilked for hundreds of millions of US Dollars (the currency upon which the back-end of the travel industry is based).
The carriers, after wrestling multi-million refunds from the GDS/CRS, then implemented stricter ticket accounting systems.
Meanwhile down at the Travel Agent level, many discovered they could earn 'points', 'credits', 'awards' by ticketing through GDS/GRS. As the Agency accounting was still done by the GDS/CRS, the TA's (Travel Agents) were able to scam the Res systems because of their weak accounting software by booking travel for fictitious PAX (passengers).
These 'ghost bookings' were cancelled and the TA's still earned their benefits! Scammers scamming the other scammers.
Around this time, about 15 years ago, I was involved in developing/installing Agency automation so that the Agents became as technologically advanced as the rest of the ticketing system.
Our software revealed that Agencies were getting ripped off by the GDS/CRS by way of omitted ticketing credits.
I believe in transparency and a trade paper was alerted to this fraud. A court case filed by a GDS/CRS based in Chicago, and founded by United Airlines, sued a Toronto Travel Agency and, as a sidebar, obtained an Order from the court that prohibited me from revealing what I knew about GDS/CRS scams - effective only to the 12-mile limit surrounding Canada. I no longer live in Canada.
The case was settled on agreed terms and SEALED. As a Petty to the proceedings I was entitled to documents which can be found on the InterNet.
As for 'main frame', perhaps someone could explain how a hundred or so PCs in Denver, Colorado, on which a GDS/CRS was using as a central system meets the definition.
For security and most privacy, out of Amadeus, Galileo, Sabre or Worldspan (they use many other names, too) I ONLY use AMADEUS which is based in Madrid and therefore the EU data rules. They have central sites in Madrid (Corporate Headquarters & Marketing), Nice (Development) and Erding (Operations).