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Sleeping beauty bitcoin wallets wake up after 14 years to the tune of $2 billion
(www.morningstar.com)
This is a most excellent place for technology news and articles.
Considering that you'd need a paradigm-breaking revolutionary and incredibly expensive device to do so, I'd find it hard to believe that you could stay under the radar with it.
What I'd expect to happen is that some big corporation and/or university manages to build a quantum computer capable of breaking 256bit encryption, and quite instantly after the announcement bitcoin will tank into nothingness or will change the algorithm to something quantum-computer safe. Well before some shady actor will get their hands on a quantum computer to crack wallets.