Via eavesdropping, terror suspects nabbed | csmonitor.com:
"But terrorists found a new system that enabled them to use phones that were difficult, if not impossible, to track.
SIM cards, for Subscriber Identity Model, were developed to create a universal - and cheaper - cellphone system. Under the old approach, a resident from, say, Britain would be charged at a local rate when making cellphone calls in England. But if he were to travel to Germany, he would be charged long distance rates. Under the new system, he can buy a German SIM card - which contains a fingernail-sized computer chip - and make the same calls at local rates.
The information on pricing, minutes, and local telephone numbers is encoded in the chip. But since there is no need for a local record of the purchaser's name and credit information, as there is when setting up a land line or a traditional cellphone account, it makes it easier for people to use phones undetected.
'What we're seeing is that people who want to remain invisible to law enforcement are doing things like this in order to evade interceptions,' says a telecommunications engineer who's helped develop ways to track cellphone users. Still, he adds, 'this doesn't make you immune from interceptions.'
After years of tracking terrorists, investigators have amassed a large database of land-line and traditional cellphone numbers they are watching (or listening to). All it takes is a call from one of those numbers to a phone with a SIM card to discover who's using the undetectable phone.
How one arrest happened
This is what led investigators to Khalid Sheikh Mohammed, the mastermind of the 9/11 plot, who was arrested in Pakistan in March 2003. A suspected terrorist whom German authorities were watching placed a call to someone with a cellphone in Pakistan on April 11, 2002.
No one spoke. But authorities said the call was made to alert Mr. Mohammed that an attack on German tourists visiting Tunisia was about to take place, which it did, later that day. Authorities began tracking the SIM card, which Mohammed supposedly moved from phone to phone, creating problems in locating his position.
But pinpointing the location of the phone was much easier. Investigators tracked it by analyzing the signals from different cellphone towers. The time it takes a signal to 'propagate and return back tells how far the cellphone is from the tower,' says an engineer. The reason the red lights flash so quickly in the Saudi command and control center is that 'the timing is nearly simultaneous,' he says."
"But terrorists found a new system that enabled them to use phones that were difficult, if not impossible, to track.
SIM cards, for Subscriber Identity Model, were developed to create a universal - and cheaper - cellphone system. Under the old approach, a resident from, say, Britain would be charged at a local rate when making cellphone calls in England. But if he were to travel to Germany, he would be charged long distance rates. Under the new system, he can buy a German SIM card - which contains a fingernail-sized computer chip - and make the same calls at local rates.
The information on pricing, minutes, and local telephone numbers is encoded in the chip. But since there is no need for a local record of the purchaser's name and credit information, as there is when setting up a land line or a traditional cellphone account, it makes it easier for people to use phones undetected.
'What we're seeing is that people who want to remain invisible to law enforcement are doing things like this in order to evade interceptions,' says a telecommunications engineer who's helped develop ways to track cellphone users. Still, he adds, 'this doesn't make you immune from interceptions.'
After years of tracking terrorists, investigators have amassed a large database of land-line and traditional cellphone numbers they are watching (or listening to). All it takes is a call from one of those numbers to a phone with a SIM card to discover who's using the undetectable phone.
How one arrest happened
This is what led investigators to Khalid Sheikh Mohammed, the mastermind of the 9/11 plot, who was arrested in Pakistan in March 2003. A suspected terrorist whom German authorities were watching placed a call to someone with a cellphone in Pakistan on April 11, 2002.
No one spoke. But authorities said the call was made to alert Mr. Mohammed that an attack on German tourists visiting Tunisia was about to take place, which it did, later that day. Authorities began tracking the SIM card, which Mohammed supposedly moved from phone to phone, creating problems in locating his position.
But pinpointing the location of the phone was much easier. Investigators tracked it by analyzing the signals from different cellphone towers. The time it takes a signal to 'propagate and return back tells how far the cellphone is from the tower,' says an engineer. The reason the red lights flash so quickly in the Saudi command and control center is that 'the timing is nearly simultaneous,' he says."
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