The terrorists who attacked Mumbai were able to thwart security agency attempts to monitor their communications by using an internet telephony service similar to Skype, the free tool used by millions of ordinary web surfers, Indian officials have said.

Mumbai police say the gunmen who occupied the Taj Mahal Palace and Oberoi hotels and Nariman House, the site of a Jewish outreach centre run by the ultra-Orthodox Chabad-Lubavitch movement, were able to contact their handlers using Voip (voice over internet protocol) telephones during the three-day siege that ensued.

These Voip phone calls could not be tapped in the same way as ordinary mobile calls and provided crucial support to the terrorists, police say. One of the gunmen inside Nariman House is thought to have contacted a leader in Pakistan as his resolve was flagging. He was read verses from the Koran and told to carry on fighting. Six people – all foreign Jews -- died inside the building.

The use of Voip technology by the militant cadre, who claimed more than 170 lives in all, fits in with a new trend towards "tech savvy" terrorism identified by military experts.

The Taleban in Afghanistan reportedly use Skype to evade eavesdropping by Western spies. Meanwhile, Palestinian militants have used Google Earth, the satellite imaging service, when targeting rocket attacks at Israel. The same free internet service was used by insurgents in Basra, Iraq, when they targeted a British Army base there.

No service, it seems, escapes attention by intelligence agencies. A recent draft US Army intelligence paper - entitled "Al Qaida-Like Mobile Discussions & Potential Creative Uses" - mulled over the possibility of Twitter, a tool that allows people to update blogs from their mobile phones, being used to co-ordinate terrorist ambushes.

The ten heavily-armed gunmen who stormed India's commercial capital on November 26 fit the profile of the modern technology literate militant, according police.

As well as using a Voip service, the group appears to have used complex GPS systems to navigate to Mumbai by sea.

They communicated by satellite phone, used mobile phones with several different Sim card, and may have monitored events as the siege unfolded via handheld Blackberry web browsers.

The terrorists also familiarised themselves with the streets of Mumbai's financial capital using satellite images, according to police. A petition has been filed in the Bombay High Court to ban Google Earth and other such services across India in the wake of the attacks.

The turning of innocent internet tools to sinister means had long been foreseen. Three years ago, APJ Abdul Kalam, then the Indian President, said that the geographic details provided by Google Earth posed a security risk. He urged India's security forces to monitor closely the growing use of such "open intelligence".

It is unclear how the authorities responded to that warning. The Indian government has been heavily criticised for its handling of the attacks, which claimed 170 lives. Experts have said the local police force, with officers mostly armed with sticks and decades-old bolt action rifles, was ill-prepared to deal with the terrorists.

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