As onpon4 said, you need the four freedoms to properly inspect--
Freedom zero is the freedom to run the program for whatever purpose. This
allows you to observe back-doors, etc.
Freedom one is the freedom to study and modify the program. This allows you
to identify and remove malicious features in the source-code.
Freedom two is the freedom to redistribute the program, verbatim.
Freedom three is the freedom to redistribute modified versions of the
program. This allows you to give others non-malicious versions of the
program.
Without all four, you can't inspect and make sure the program does what you
want it to do.
For example...
Without freedom zero, perhaps it could be illegal for you to run the program
for the purpose of identifying holes. (It is commonly easier to find security
holes by running the program than reading the source code.)
Without freedom one, you wouldn't be able to do anything with the malicious
program, and you'd have to deal with it.
Without freedom three, you would be the only one with a non-malicious version
of the program. You wouldn't be able to help anyone else.
