You're absolutely correct sir, that password was entered to protect that Imac from unauthorized access. Your best bet it to take it back to where you bought it from and get it cleared. It's a mid 2010 machine and still under warranty and someone put that password in less than nine months ago. I'm sure you registered it with Apple and they will be able to give you entry to the machine. Just contact them here anywhere in the world: http://support.apple.com/kb/HE57
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Please don't get angry with me if the hardware and the software are doing what was intended by Apple and not allowing unauthorized access.
You're absolutely correct sir, that password was entered to protect that Imac from unauthorized access. Your best bet it to take it back to where you bought it from and get it cleared. It's a mid 2010 machine and still under warranty and someone put that password in less than nine months ago. I'm sure you registered it with Apple and they will be able to give you entry to the machine. Just contact them here anywhere in the world: http://support.apple.com/kb/HE57