Had a co-worker who used his admin rights to break into e-mail accounts of senior management personnel. I found out about it after he'd been fired for it.

I used to work for a bookstore. A few months after I left, I found out from a former co-worker that the regional manager had fired the whole store's management team, and they had retaliated by using a loophole in company policy to sell every book in the store to the employees they liked for 1 cent. Not 1 cent per book, 1 cent for the whole contents of the store. Apparently it was one huge cash-register receipt.

Another place I worked, an employee stole another employee's credit cards out of her purse, used them to purchase pharmaceuticals online, and set the front desk of the company as the delivery address (more than slightly dumb). Upon further investigation, the managers there found out that the reason she'd been on the job market is because she had been fired from a local school district for abusing the children, and was actually pending trial on criminal charges related to that. Background checks didn't show this, because she hadn't been tried yet (innocent till proven guilty and all that).

I have a friend who once arrived to work to find sheriffs manning the doors. They wouldn't let anyone take anything from their desks unless they could reasonably prove it really was their personal property. Turned out some of the business partners had been embezzling funds, and some employees had benefited from this in terms of "personal property paid for by the company". The business was shut down and people were prosecuted.

So, yeah, there are ethics issues out there. Keep you own nose clean, help others to do so, report criminal stuff, and try to keep from getting burned. If you want to do more, you can, but it's not pretty.