In November last year, researchers Joe Grand and Bruno, using insights into a flawed password generator, successfully cracked an 11-year-old password, unlocking Michael's $3 million cryptocurrency wallet initially thought irretrievable.

When "Michael," a cryptocurrency owner, reached out to Joe Grand two years ago asking for assistance in regaining access to almost $2 million worth of bitcoin that Grand had kept on his computer in an encrypted format, Grand declined.

Michael, a Europe...