Hello my Chromebook appears to run a script that dynamically alters files I download for e-mail.

Hello,

My chromebook appears to run a script that dynamically alters files as they are downloaded.  Yes yes, I understand your position will be something to the effect of "This is not possible" but I can only tell you from my perspective what is happening.  Is this a factory setting?  How can I turn it off. Or, should I be concerned that it is a spy from a Communist Block Country messing up the works. That perhaps, I should have registered my machine when I bought it because it's been supplanted with an idential looking product, similar in all ways with the exception that there is a mirrored hard drive in the unit which spins up under radio command to act as a traditional computer, simultaneously housing key logging software AND script capable.

Thoughts?

Thanks.