Русская версияThe loss of thousands of criminals' details has prompted a demand by the Information Commissioner's Office for "searching questions" to be answered.
The missing memory stick includes un-encrypted details about 10,000 prolific offenders and data on all 84,000 prisoners in England and Wales.
Shadow Home Secretary Dominic Grieve said he was "absolutely horrified" by the loss and "government incompetence".
The Home Office said a full investigation was being conducted.
A spokesman said the data was lost by private company PA Consulting and was "held in a secure format on site and downloaded onto a memory stick for processing - which has since been lost".
PA Consulting has searched its premises and looked at CCTV recordings in an attempt to recover the missing memory stick.
It the latest in a string of lost data incidents for the government, including stolen laptops, lost computer discs and memory sticks and files left on trains.
This time, the Home Office was first told by PA Consulting on Monday that the data might be missing.
The contractor confirmed on Tuesday it had failed to uncover the memory stick, but it was not clear how it came to be lost.
The data on the stick also includes information from the Police National Computer of some 30,000 people with six or more convictions in the last year.
Details of serving prisoners included names, addresses, dates of birth and in come cases release dates.
The transfer of further data to PA Consulting on the project has been suspended pending the investigation.
'Toxic liability'
David Smith, Deputy Commissioner in the Information Commissioner's Office, said the latest loss showed that personal information could be a "toxic liability" if not handled properly.
"It is deeply worrying that after a number of major data losses and the publication of two government reports on high profile breaches of the Data Protection Act, more personal information has been reported lost," he said.
He added that data protection needed to be taken seriously at all levels and sensitive information, such as prisoner records, held securely at all times.
Mr Smith said: "We expect the Home Office to provide us at the Information Commissioner's Office with a copy of the [internal investigation] report and its findings.
"We will then decide what further action may be appropriate. Searching questions must be answered about what safeguards were in place to protect this information."
Shadow Home Secretary Dominic Grieve said the Home Office "has a habit of doing this".
He said: "It's entrusted with a great deal of highly confidential material and it seems to be entirely incapable of keeping it secure.
"And the consequences are very serious. They're serious because it may lead to the identity of the people involved being revealed."
"One of the possible consequences is that they [criminals] will bring legal actions against the government and the taxpayer will then have to pay damages to people, who appear to be pretty undeserving, because of the government's incompetence."
A spokesman for PA Consulting refused to comment on the data loss at the Home Office.
Earlier this month the BBC apologised after a memory stick containing the personal details of hundreds of children who had applied to take part in a TV show was stolen from a vehicle.
On Tuesday, a BBC analysis found sensitive data potentially affecting more than four million people had been lost by government departments in the year to April.
Cases included the loss of the National Insurance numbers of 17,000 people and the theft of a laptop with encrypted details of 17,000 Sats markers.
The details of 25 million child benefit claimants vanished last year.
The incident led to the recommendation that government departments should give details of personal data losses.
(BBC)
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