Personal data belonging to thousands of wealthy Russians, including names, home addresses and mobile numbers, has been leaked online.
Up to 24,500 well-to-do Muscovites whose information has been compromised are all clients of Moscow-based internet provider Akado Telecom, a large telecommunications network owned by billionaire businessman Viktor Vekselberg.
The data includes the mobile phone numbers and addresses of a high-ranking Russian government official, a well-known film director and a leading businessman's relative, said the Reuters news agency, which saw hundreds of the records.
The data was uploaded to the database of RIPE NCC, a not-for-profit regional internet registry for Europe, the Middle East and parts of Central Asia.
RIPE NCC has a public database that lists which IP addresses have been allocated to different internet service providers – but does not normally identify individual customers by name or other personal information.
The firm's communications director, Aleksei Semenyaka, said companies on its registry load their own data onto the database, meaning Akado must have uploaded the details, which he confirmed could be accessed freely.
Akado Telecom said it had launched an internal investigation, but failed to confirm whether it knew its clients' private data had been compromised or if it had provided the information.
The company said in a statement: "We always respond to criticism with attention and gratitude and conduct thorough analyses to uncover vulnerabilities in our information systems in order to prevent possible data leaks."
Most of Akado Telecom's 24,500 users live in the Russian capital's wealthiest districts.
Government agencies and banks that use Akado Telecom also had information uploaded, as well as the contact details of Akado's own staff.
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In Russia, it has been illegal to make personal data publicly available since 2006 and companies breaking the law can be fined up to 50,000 roubles (£598).
Russian authorities have been paying close attention to such incidents following leaks that led to the publication of information about military intelligence agents accused of links to an attack on former Russian spy Sergei Skripal in Britain.