Suppose I have a web service used for increment/decrement uses' refos.

It may has these fields: 

action: increment/decrement
refos: 1000

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The problem is, how can I know whether it's sent from firebug by a programmer or from my system?

I should respond to the action only if it's from my system.

The context is actually in a web game, where my system should increment the user's refos when some task is finished. But how do I deal with faking?

In reply to A question about web service security by Anonymous Monk

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