Profesional ethicas reffer to on the job choices and actions that reflect the persons valuse.
Try and forget what you have seen, Or in some cases report suspicious activity like harassment and divulging information to other companies.
Some work you may be doing might conflict with privacy laws you could refuse to do it based on what you think of it.
To make sure you don't violate this stay up to date on copyright.
Some people might try and take advantage of the trust they have been given by disclosing information about the company they have been given. (Example Medical or financial information)
Check business plans of prospective employers to make sure that you don't have to work on projects that directly compete with the company you just left.
Make sure you know your employers policy for personal use so you don't get you self in a deilmma like using computers to develop software and have them claim the rights to it.
To not get in trouble simply don to any hacking.
But they don't know if they could control it so its a good idea to stay away from it.
Make sure the software you release it up to your standers before you release it so you don't have any problems with it in the future.
You should make sure you think the software will be used for legal purposes when you make it and if their are nay questions about it you should think carefully about it before you release it.