Class action might be a solution for US citizens. The problem with malware though is that you end up infecting a whole lot of innocent civilians all over the place, which the people in Den Haag have slightly mixed feelings about. To be honest, I'm a bit disappointed that these cases never end up in international courts. The rules we have in place seem pretty clear to me.
AFAIK there are no widely accepted international conventions that would forbid, say, USA goverment to install malware (intentionally or unintentionally) on a german user's computer; if you can name as specific one then that would make this discussion much more interesting. International law is not particularly restrictive to the rights of governments to attack each other or their citizens if they desire so; the citizens don't have much recourse in international courts if a foreign government accidentally killed them, much less damaged their computer.
Given that you've used Germany as an example, I'd recommend this german podcast to you which explains the legal surroundings in great detail: http://alternativlos.org/25/
