A laptop containing confidential information about 11,000 patients has been stolen from a Wolverhampton GP's home.
Contrary to Department of Health guidelines, the information was not encrypted, which would have made it unreadable without a special code to unscramble it.
The laptop was among items stolen in a recent burglary at the home of the unnamed doctor, who works at the Castlecroft Medical Practice.
The information on the computer, which belongs to the practice, included patients' names, dates of birth, addresses, contact details and confidential medical records.
The practice has written to all of its 11,000 patients to inform them that information about them was on the stolen computer.
Dr Peter Wagstaff, senior partner at the practice, said: "The practice is treating this issue very seriously and we are extremely sorry for any distress or concern that it may cause our patients.
"Though not encrypted, the confidential information on the laptop was protected by a complex password system, which only a person with specialist computer knowledge would be able to crack."
He said the laptop appeared to have been stolen for its re-sale value, rather than for any information stored upon it.
Jon Crockett, chief executive of Wolverhampton City Primary Care Trust, said: "Patients and the public have the right to expect that those dealing with confidential information maintain the highest levels of security and we are carrying out a full and urgent investigation into this incident."
He said that the practice had believed that the laptop was encrypted, but it later found "this was not the case".