The US government has never officially confirmed the existence of Echelon, but an investigative committee of the European Parliament recently concluded that the spy network is real.
"Echelon can intercept any communications worldwide. If there have been phone calls or faxes, this system should have intercepted it. If there have been communications, it was done under a cover of encryption or by old-fashioned courier" said Elly Plooij-van Gorsel, Dutch MEP and vice-chairman of the committee.
"Technology is not a solution, but a race. Terrorists also have technology. Intelligence services worldwide have to cooperate with technology as a tool. Information is currently shared on a bilateral basis, but there is no real cooperation," she said.
Echelon, which is thought to be operated by the US National Security Agency (NSA) and intelligence services in Canada, the UK, Australia and New Zealand, is probably being used in the hunt for the perpetrators of the attacks in the US.
Other observers commented that technology might not have been a good investment for intelligence services.
"There has been an intelligence failure," said Peter Sommer, senior fellow of the computer security research centre at the London School of Economics. "Is that because some aspects of [security] have been overplayed at the expense of others?
"The area that is interesting is this question of the role of electronic surveillance. There is bound to be a wholesale re-evaluation of intelligence doctrines. There is likely to be a continuation of the debate of funding for [surveillance technology] at the expense of older types of spying."
He added: "We need intelligence assets and human assets; people who can infiltrate these groups. We have moved into a more dangerous world now. There will be another set of arguments that say that we have undervalued the role of human intelligence."