I forgot my security code for nokia 1680c-2 IMEI no. 356782/02/856888/2

Yes , the phone has to be reset as no codes will be excepted. You will need to reinstall, check and estimate.

SECURITY CODE:

If you are talking about the security lock code to enter into the phone then once it is lost nothing can be done except flashing the mobile . Because if anybody can give the security code created then who ever who steals your phone can get into it and get your valuable information.

So as safety precaution to avoid that they have designed it such that if you forget the security lock you have to reset the mobile memory by flashing the mobile at an authorized service center.So while flashing the mobile all the data in the mobile memory will be lost and you can again start using the mobile.