If you don’t already know, piggybacking is somehow hacking into another person’s Internet connection so you can use it yourself. There is some way to divert the connection from another computer to your own as well. This is basically using someone’s Internet connection without their permission. I know this is immoral, but how much so? Is it a mortal sin? (Strangely, however, I don’t think piggybacking is illegal).
Yes, it is objectively problematic to use someone’s Internet connection without that person’s permission. The status of the matter would depend on how serious the damage was that you caused using that person’s connection. Adding a few extra pennies to the credit card bill during a one-time “joyride” on another person’s connection would probably be venial. Racking up a huge bill, continually adding to that person’s bill over an extended period of time, or using your access to damage that person’s credit or reputation would make the matter far more serious.
Whether or not the action is currently illegal makes no difference to the objective morality of the action, although I doubt that it will remain “legal” for long. I suspect that, if they haven’t done so already, lawmakers will catch up to the practice soon enough.