Why can you be ethical to your coworkers and not your employer? You boss is a living being too, and he is working for the company just like you are, even if his status is different. And your coworkers are the ones who make up the company, so being ethical to your coworkers is being ethical to your company.

And if filing your computer causes a problem to your IT department for whatever reason, and you do it without approval, then I think it is indeed not very ethical, it really depends on the situation. The IT department people are your coworkers too.