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Pro-Putin hacktivists KillNet in a Telegram post claimed responsibility for crashing the Buckingham Palace website.
Daily Mail reported same group gave threats to NHS and had launched cyber-attacks on Eurovision and JPMorgan.
Interestingly, the hack was launched just days after King Charles condemned the invasion of Ukraine with a distributed denial of service (DDoS) attack.
KillNet group formed around March 2022, and supported Russia and its invasion of Ukraine.