A council is investigating the theft of four laptops containing the personal details of more than 14,000 voters.
One of the computers contained names, addresses, dates of birth, signatures, copies of scanned postal vote application forms and postal vote statements.
St Albans City and District Council said the information was not encrypted, but was password protected. The council has written to voters affected because, it said, "there is a small though unlikely risk, of the data being accessed and used fraudulently".
The council said there was no evidence of a break-in at the council offices and that it was likely to have been an opportunistic theft.
The Electoral Commission and the Information Commissioner's Office have been informed of the theft. An internal investigation is also been carried out to find out whether there's a need for further security. The council added: "We are working with the police and Northgate Information Systems, who manage the council's information technology services, to find out what happened."
St Albans is not the first council to lose data - a large number of public sector organisations have experienced similar problems over the past couple of years. The council advised voters to be careful about giving out further personal information to anyone.