Around 7,000 members of a teachers union have been hit by a data breach following the loss of personal details on a laptop and USB stick.

Personal details of members of the Association of Teachers and Lecturers (ATL) were contained on a laptop and USB stick that was lost or stolen from the roadside as an ATL member was packing his car.

The laptop was the property of the ATL and contained the personal details of 6,282 union members; it was not encrypted but was password protected. The memory stick, which was not password protected or encrypted, belonged to a staff member and contained 3,366 of the same records on the laptop.

The ICO found the ATL to be in breach of the Data Protection Act. The ATL general secretary Mary Bousted has signed an undertaking to ensure that by 28th February 2010, all portable and mobile devices used to store and transmit personal details are encrypted.

The undertaking also requires a review of the policy covering the transfer and storage of personal data. Staff will need to be made aware of this policy and prohibited from storing personal information on their own memory sticks.

Mike Bienvenu, technical director of Softek, said: “This is a lot of people and thinking about data, could this include bank account details? Presumably the union will write to its members to inform them and they may have to change bank accounts. People know about controlling devices and it is not new technology.”

Sally Anne-Poole, head of enforcement at the ICO, said: “I encourage organisations to prevent staff from downloading large amounts of personal data. It is vital that portable devices, including laptops and memory sticks are encrypted if they are used to store personal information.

“Staff members should not be allowed to keep people's personal details, especially sensitive personal information, on their own memory sticks. I am pleased that the ATL is taking remedial steps to prevent a similar situation occurring again.”

The announcement comes two months before the ICO will be able to impose fines of £500,000, as it announced at the beginning of this year.