(CNN/MONEY) — The number one way hackers get into protected systems isn’t through a fancy technical exploit. It’s by guessing the password.

That’s not too hard when the most common password used on business systems is “Password1.”

There’s a technical reason for Password1′s popularity: It’s got an upper-case letter, a number and nine characters. That satisfies the complexity rules for many systems, including the default settings for Microsoft’s widely used Active Directory identity management software.

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