Well, there are hundreds of methods to protect you EA:

1- You can use the code I submitted (hard coded password).
2- You can make an algorism to collect something and compare it to the password. (For example: the account margin x date of purchase / 100).
3- You can create a dll and ship it with the EA and the dll will handle the password (it can connect to your web site and get the password).
4- You can tie the EA with the account number of the user. You ask him by email to give you the account number then you but it in the EA and compile it then send the compiled version to the user.
5- You can the EA works with a specified MT version only.
6- You can limit the numbers of running of the EA.
7- You can limit the days of using the EA.

8- You can share the EA for free and ask the user if he like it to donate you. REOMMENDED