VeriChip -- and other vendors -- have been busily implanting radio-frequency ID (RFID) chips in human and animal subjects ever since the FDA approved the process. But a series of studies conducted from 1996-2006 noted a high incidence of dangerous tumors arising at the sites of RFID implants -- something the FDA apparently did not consider when it approved the procedure.

Cancer or no, I wouldn't go near an RFID implant. These things don't have off-switches. They don't have disclosure policies. They don't have logs, or even notifiers. That means that you can't stop people from interrogating your RFID, you can't choose who gets to interrogate your RFID, you can't see who has polled your RFID -- and you can't even know when your RFID is being read. You wouldn't carry normal ID that behaves this way, but from London's Oyster Card to the DOT's FastPasses to the new US passports, these things are being stuck to our person in ever-greater numbers.

And while manufacturers claim that these things have inherent security because they can only be read from a few centimetres away, hackers have already ready them at more than 10m distance.

Leading cancer specialists reviewed the research for The Associated Press and, while cautioning that animal test results do not necessarily apply to humans, said the findings troubled them. Some said they would not allow family members to receive implants, and all urged further research before the glass-encased transponders are widely implanted in people.

To date, about 2,000 of the so-called radio frequency identification, or RFID, devices have been implanted in humans worldwide, according to VeriChip Corp. The company, which sees a target market of 45 million Americans for its medical monitoring chips, insists the devices are safe, as does its parent company, Applied Digital Solutions, of Delray Beach, Fla.