A year-long experiment that baited hackers to try and break into systems netted an interesting result: A single letter, x, was one of the most common password guesses.

Rapid7, an IT security company, set up honeypots that were designed to mimic systems running RDP (remote desktop protocol). The protocol is used to remotely login into a system and is often run by POS (point-of-sale) devices, kiosks and other Windows systems.

Attackers often scan the Internet to find RDP systems and then try to log in. Rapid7 logged more than 221,000 login attempts and then studied the credentials that attackers used.

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