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The personal information of an unknown number of serving UK military personnel has been accessed in a significant data breach, the ´óÏó´«Ã½ understands.

The hack targeted a payroll system used by the Ministry of Defence, which includes names and bank details of both current and some past armed forces members.

In a very small number of cases, the data may include personal addresses.

It is unknown who is behind the hack or what the data may be used for.

The data, described as "personal HMRC-style information", relates to current and former members of the Royal Navy, Army and Royal Air Force over a period of several years.

The system was managed by an external contractor and no operational MoD data has been obtained.

It is understood the MoD has taken immediate action and the system has been taken off-line, while investigations are under way.

The MoD is in the process of notifying and providing support and advice to those affected, including making veterans' organisations aware of what has happened.

Defence Secretary Grant Shapps is due to update MPs about the hack in the Commons on Tuesday.

He is expected to set out a "multi-point plan" in response, which will include action to protect affected service men and women.

While it has not been disclosed who is behind this hack, it comes amid increased warnings about cyber-security threats facing the UK from hostile states and third parties.

Last year, the government published an updated version of its long-term defence which said the use of "commercial spyware, ransomware and offensive cyber capabilities by state and non-state actors has proliferated".

In March, the government publicly accused China of being behind an August 2021 hack targeting the details of millions of voters held by the Electoral Commission.

In December 2023, the National Cyber Security Centre said Russian intelligence was behind a "malicious cyber activity attempting to interfere in UK politics and democratic processes".

Public institutions and private firms have also been targeted by hackers demanding ransoms.

The Metropolitan Police said it is not involved in any investigation at this stage.