I would challenge the concept of the government carrying out "legitimate surveilance" through this dubious means.
The person surveiled has not been has not convicted of a crime yet the state has taken onto itself to install software that would leave the person open to further hacking by random individuals.
This is akin to the police not simply breaking into the house of a man they suspected of a crime but also them leaving his door a-jar after they left. See the Sony Rootkit.
If they got a warrant first I'd be OK with it - as long as they were competent of course and didn't leave the person vulnerable.
It's no different from getting a warrant for a phone tap, or a copy or your US mail.
(Incidentally they don't need a warrant for a copy of the address on the front, called http://en.wikipedia.org/wiki/Mail_cover - so presumably they don't need a warrant to ask your ISP for a list of IP address, but I'd want a court to confirm that first.)
What in my post lead you to believe I thought that governments don't engage in a variety of dubious surveillance (including surveillance which leaves open back doors to the victims machine)? They certainly do.
The thing is that exposing these acts and fighting all efforts to make such acts legal is still important for limiting how much the state can do.
The person surveiled has not been has not convicted of a crime yet the state has taken onto itself to install software that would leave the person open to further hacking by random individuals.
This is akin to the police not simply breaking into the house of a man they suspected of a crime but also them leaving his door a-jar after they left. See the Sony Rootkit.