Farmers and landowners are being urged to remain vigilant after animal rights activists leaked the addresses of thousands of gun owners in the UK.
An online map was published that claimed to show the addresses of over 110,000 gun owners across the country.
Authorities are now investigating the data breach, which has been linked to UK firearm merchant Guntrader.
It saw 111,295 Guntrader users' details leaked in July, with animal rights activists sharing the information on a blog, according to The Register.
Animal rights campaigners had then published instructions on how to link the Guntrader data with online mapping software.
The National Crime Agency (NCA) has responded with details of the ongoing investigation and provided advice on how gun owners, such as farmers and landowners, can increase their vigilance around security.
An NCA spokesperson said: “The NCA is aware that information has been published online as a result of a recent data breach which impacted Guntrader.
"We are working closely with the South West Regional Cyber Crime Unit (SWRCCU), who are leading the criminal investigation, to support the organisation and manage any risk.”
The British Association for Shooting and Conservation (BASC) has asked firearm owners to remain vigilant and report any concerns to the police.
Martin Parker, BASC’s head of firearms, said: “We will remain in contact with the NCA and SWRCCU as the situation develops and we are pressing to ensure the agencies get to the bottom of this.
"It was already a significant breach of data, but this latest development is particularly concerning.
“In the meantime, we are sharing the security advice issued by the NCA and ask members to remain vigilant and report any concerns to the police.
“We also advise against clicking on any link purporting to show the data as it could include malware that could infect your device.”
In addition, the NCA has informed BASC that they have made all firearms licensing units aware of the breach and confirmed the Information Commissioner (ICO) is aware of the issue and is in contact with Guntrader.
In their response to BASC, the NCA said: “In order to assist law enforcement in mitigating any impact on the public, it is important leaked information is not shared, or drawn attention to, by the media.”