Can a company Hack Back? Is it legal, or vigilante justice?

Victims of Cyberattacks may attack their attackers by doing the following. But is it legal?

Instead, the company pretends it’s going to negotiate. They fool the blackmailer into downloading a file. “Tell them we need to communicate securely,” Liu explains. “Tell them, ‘you need to use this encryption program.’”
The blackmailer installs the software and, suddenly, “you use it to push back into their system, get into their laptop, figure out where they are.”
That is, the victim goes inside the invading server.

Source: Hack Back?

Tech debate: Can companies hack back? | Al Jazeera America

Thanks Jacques
Steve