I think this subject needs some serious legal information references. As I've been researching through simple google searches I've seen that most people believe you generally are not allowed to legally relatiate. You will need to check your local laws but here in the US it varies by state, my state (Texas) talks about self defense in this form
"Self defense.
(a) Except as provided in Subsection (b), a person is justified in using force against another when and to the degree he reasonably believes the force is immediately necessary to protect himself against the other's use or attempted use of unlawful force.
" -
http://answers.yahoo.com/question/in...2120258AAuJ5f5
So I'm no attorney but that says to me that if you catch someone actually damaging your personal property then you can use force back in defense. Now I'm sure it wouldnt hold up in court if they hacked into your WIFI and you break into their machine establish a reverse shell and start deleting system files and say that was self defense. But if they have broken in and established a reverse shell in your system and are planting virus's, trojans, or possibly deleting files from your computer or i've heard some people will use your printer and print out random things, you can defend yourself by breaking into their machine and rendering them incapable of continuing with the destruction through whatever means necessary (since physical injury is not an option).
Now this is Texas Law so I was just stating it as an example.