Durham County Council has reassured citizens that no harm has been caused by the loss of a memory stick containing personal data belonging to pensioners served by the local authority's telecare service.
Care Connect, Durham's community alarm and telecare service, is designed to help vulnerable people maintain independence in their home, providing about 3,600 elderly and vulnerable residents 24-hour assistance.
The encrypted memory stick, which was lost in May 2013, contained key safe codes, details of personal needs and contacts for those involved in the Care Connect scheme.
Key safes, opened with an access code, are secure places holding house keys to allow care wardens to enter a house if the resident cannot get to the door.
Adrian White, head of contract services at Durham County Council, said: "I would like to reassure everyone who uses the Care Connect service that there is absolutely no cause to be concerned.
"The memory stick was fully encrypted, in line with government data protection guidance, to ensure that anyone outside the service would not be able to access the records."
He added that the key safe codes were quickly changed once the loss was reported.
"It is good practice to change key safe codes on a regular basis and we were about to start a programme of changing codes when the encrypted memory stick was lost. We brought forward this work as an additional security measure."
The Information Commissioner's Office has not yet replied to a request for comment on the data loss. Breaches of the Data Protection Act (DPA) can lead to financial penalties.