Lock field automatically after data is entered

[Guest_imported]

I am looking to create a form where once data is entered into the field it is automatically locked so that the information cannot be changed. Is this possible? Or can I set certain passwords where some fields are locked when using one password but not when using another?

Thanks for any help

 

[cainemart]

After the field has data in it(gotfocus) and the user moves to the next field(lostfocus), set the locked property with code.