I forgot my password I had set a security password on my Samsung Galaxy S Duos mobile and unfortunately forgot the unlock password. I tried hundreds of times to unlock my phone with many possible passwords but was unsuccessful in each of my attempts. Please help me unlock my phone and send me the master code (if any) to unlock the phone.
Go to https://www.google.com/android/devicemanager

Provided you have your phone set up with your Google account, it should show up on that page. Choose the LOCK option. It'll ask you to set a new pincode (and message if you want). As soon as you hit "lock" after entering in the new pin, the phone will lock with the new pin. Now just try to unlock your phone again. 

That feature is really supposed to be a way to remotely lock your phone if it gets lost/stolen and doesn't already have a pin/password lock on it, but its a handy little workaround for resetting your pin if you forgot it.

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Another option is through Samsung's Find My Mobile site.
The guide for your model shows two possibilities:  


Lock my device: Locks your device by setting a 4 digit PIN to prevent
other people from operating your device.

Unlock my screen: Initializes the security lock settings such as the screen lock pattern, password and PIN to unlock the screen of your device.
Since this function initializes the device's screen lock setting, you must set the screen lock setting again. The screen lock set by the device or remotely set by the Lock my screen function will be released.
 


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If none of this works, I'm afraid you may be looking at a factory reset.