Windows XP was a big hit, but had its security problems
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Although the former was launched way back in 2001, a completely different era in computer history, there are still many machines around the world running the OS with the green start button. In Armenia, the OS was the most popular we believe in 2021, and it is not over in the US either: in 2019, it was discovered that one in three companies still ran at least one machine with XP. And in February 2015, we reported that "Windows XP has increased by over 5 percentage points."
It is The Register that recently discovered a blog post in which it is revealed that Windows XP's method of validating serial numbers can be done with Linux.
Made it offline in 2019
So this is the algorithm, including the method for approving serial numbers. Windows XP has of course been pirated since its launch, but not by approving its own serial number, but by deceiving the activation.
And because they now know the secret recipe of Microsoft, the keys can be authenticated without an Internet connection (XP could be hacked with almost the same method in 2019, but then an Internet connection was required), which should be where the OS remains. Support for the OS in the form of new security updates stopped in 2009, so the chance of the OS being infected is high, and from there other machines on your network can be infected.
As an FYI, we are told that the phone activation service for Win XP still works, so that may be an option.