Is it considered "theft" or "stealing" if you don't keep what you steal?

Yes, but technically "theft" is not a crime or a tort (a civil wrong).  Crimes, at least in the U.S., are no longer common law, but rather codified in the criminal statutes of the applicable jurisdiction.  The acts you've described would all be crimes, but the particular crimes they would constitute depends on the particular laws of the applicable jurisdiction.  Just by way of example, the acts which may constitute larceny in the third degree in Alabama may constitute theft by trick in the second degree in Texas.  You can rest assured, however, that they would all be crimes (likely more than one crime), but it is likely that the hacking would violate different statutes than would the vandalism.  Civilly, the hacking you describe would probably constitute the tort of conversion (wrongfully exercising dominion and control over the property of another) and possibly other torts (for example, there is a New York criminal statute prohibiting hacking; the violation of that statute, in addition to being a crime, may give rise to a civil cause of action); the vandalism might also constitute conversion and would probably also constitute trespass and other torts.