Wi-Fi Protected Setup (WPS) is used to secure access to wireless networks and requires each router to have a unique eight-digit PIN.
the protocol used by Wi-Fi Protected Setup reports back after the first four digits have been entered, and indicates if they are right, which means they can be attacked separately. The last of the eight digits is just a checksum, so having got the first four the attacker only then has to try another 1,000 combinations (identifying the other three digits) and the entire PIN is known.
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