Here is a great tool to protect your php source code. PHP Encoder from phpSHIELD, converts PHP source code into unreadable bytecode, providing php script protection and compiling at a great price point.
Some other PHP encoding systems do not use bytecode and it is very easy to reverse engineer their protected scripts back to the original source code. With bytecode encryption, it is never possible to do this as the original sourcecode has been completely removed from the protected file.
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