Mobile devices contain large amounts of personal data
London taxi passengers have left more than 60,000 hand-held devices in the back of black cabs during the past six months, a survey has found.
Some 55,843 mobile phones and 6,193 other devices, such as laptops, were forgotten, Credant Technologies found.
The data protection company, which surveyed 300 taxi drivers, warned users to password-protect equipment amid rising fears of identity theft.
Fraud experts said such devices could give criminals crucial data.
New devices - including mobiles, MP3 players and memory sticks - have the capacity to store tens of thousands of documents or pictures and millions of contacts and emails, making them a target for identity theft criminals and hackers.
A survey by credit reference agency Equifax in April suggested 16% of its customers put PIN numbers on their mobile devices while 24% recorded birthday dates.
Credant Technologies said losing such personal information could be "disastrous" for individuals as well as companies, and advised users to encrypt or password-protect equipment.
Chief marketing officer Michael Callahan said: "If it gets into the wrong hands of a criminal, hacker or opportunist, losing your mobile device can have serious implications, so our advice is always encrypt it and password protect it to stop it ever being accessed by anyone other than yourself."
The survey's findings follow a number of high profile data-loss scandals, which have highlighted the risk of identity theft.
Earlier this month, the government confirmed a computer hard drive holding details of up to 5,000 justice system employees had been lost last year and in August a private consulting firm lost a memory stick containing the details of tens of thousands of prisoners.
In addition, in November last year, HM Revenue and Customs lost two computer discs containing the entire child benefit records, including the personal details of 25 million people.
Neil Munroe, external affairs director of Equifax, one of the partners in National Identity Fraud Prevention Week, said people were now losing more than just phone numbers when they misplaced devices.
"People now have PINs, passwords and email addresses on them," he said. "This gives fraudsters a good start to begin phishing."
While most people now recognised the importance of securing their laptops, many did not do the same for their mobile phones or other hand-held equipment, he said.
All should be password-protected and users should avoid storing key personal information on them, he warned.
"The moral of the story is don't put it on there if you don't have to."
Chris Mayers, chief security architect at applications delivery firm Citrix, said businesses needed to think more carefully about what sensitive data employees were carrying around outside the office and what they should be be doing to keep it safe.
"In many cases that data doesn't even need to travel. Laptops don't need to contain sensitive data," he said.
"Print-outs don't need to be ferried from pillar to post, yet it seems too many people regard sensitive data with the same careless regard they have for their umbrella."
The Credant Technologies survey also suggested the back of a cab was not such a bad place to lose a mobile device, with 80% of London taxi drivers surveyed claiming the owners were reunited with it once found.
The research also found drivers discovered other strange objects in the back of their cabs, including a sawn-off shotgun, 12 dead pheasants, two dogs, toilet seats, a casket of funeral ashes and £2,700 in cash.