How Reset Your Security Code

Install Nokia PC Suite
Install Nemesis Service Suite (NSS)
Connect your phone to your PC with data cable. If the phone ask for connection mode, choose default mode or PC Suite mode (But don't open Nokia PC Suite).
Open Nemesis Service Suite (NSS)
Click scan for new devices button (on top right corner of NSS)
Click Phone Info button
Click Scan button
Click Permanent Memory tab
Click Read button
It will read the permanent memory file and save it on the hard disk at following path. C:\Program Files\NSS\Backup\pm\.pm
Open the .pm file using Notepad
Now scroll down until field [308] and on the 5th Record (5=), your security code is saved at there.
For example, 5=31323334350000000000
Just ignore the red colour font. So, 12345 is your security code.
If this guide doesn't work with your Nokia phone, follow this guide of how to reset security code to default. The Nokia default security code is 12345.