Bluetooth mobiles can be easily hacked, letting someone steal phone books, images, calendar information, or virtually anything else stored on the phone, security experts have warned.

Adam Laurie, chief security officer and director of AL Digital and the Bunker, a secure Web hosting facility in Europe, and Martin Herfurt, a researcher at Salzburg Research, have both warned about the phones' poor security.

The pair demonstrated software tools they created give them almost total control over Bluetooth phones from a wide range of handset manufacturers, including Nokia, Sony Ericsson and TDK.

Herfurt demonstrated three different ways to attack a phone: send unsolicited text messages; download all the data stored on a phone; and turn the phone into a roaming bug by forcing a targeted phone to call another phone.

This last attack, which the pair call "BlueBugging", is potentially the most damaging because once the attacker initiates a call on the victim's phone, there's no need to stay within Bluetooth range, typically about 30 feet. The target need only be in a phone service area to be exploited.

This kind of attack could also be used to commit fraud, according to Laurie. For example, an attacker could force victims' phones to dial a phone service that bills the victim per call or per minute.

Increasingly, "phones are being used as portable data stores" Laurie warned, for information such as passwords, PIN numbers, and other sensitive data. A hack would therefore be of greater value for a hacker and trouble for the phone's owner.

"Fifty to seventy percent of the phones we see are vulnerable," Laurie said. He said security researchers from computer security consulting firm @stake has further uncovered flaws in Bluetooth encryption, which could make the danger worse.

Many users set their phones on what hackers call discoverable mode in order to use Bluetooth accessories, such as headsets, but carelessly leave it in that mode, he noted. Also, many manufacturers set discoverable mode as the default, to help customers quickly and easily connect accessories or devices.

Data theft using Bluetooth is especially hazardous because "you don't have to be visible to the person you're targeting," Laurie said. He found that he could connect to many Bluetooth devices well beyond the usual range of the wireless technology: Using just a small dongle on his laptop increased the range to about 40 meters, and some high-gain antennas could stretch communications to 90 meters.

In their presentation, demonstrating how to steal a phone book, they connected to a Nokia phone that briefly displayed a telltale message on screen but made no sound. If the owner isn't looking at the phone's screen at the moment an attacker connects, it probably won't be apparent that the phone is compromised.

Several handset manufacturers dismissed his claims as far-fetched, which prompted him to do field research, Laurie said. In one experiment, he ran his original Bluetooth intrusion program on his laptop while standing on the platform of a London Underground subway station during rush hour. He detected 336 Bluetooth-enabled phones, and deemed 77 of them "definitely vulnerable" to one or more of the attack methods. Laurie deemed a phone vulnerable if he was able to recognise the phone's default Bluetooth name, which a user can change.

Later, he conducted the same experiment inside the British Houses of Parliament. His laptop was X-rayed at security checkpoints but he then wandered through the halls of government and discovered four vulnerable phones within 14 minutes.

Phone manufacturers have a duty both to their customers and shareholders to make a safe and secure product, Laurie said. "Manufacturers who knowingly ship phones with problems have broken their fiduciary duty by doing so."