I think you should be able to be hacked at any time. On-Line or Off-Line. However, once you do get hacked you get a shield for three hours. But you can still play and hack other people and do not appear in the search.
This would have a number of positive affects on the game.
1. Stops people from being hacked multiple times in a short space of time. You could only be hacked up to 8 times a day.
2. Stops people from effectively locking their account by being on-line all the time.
3. Only people who you are able to hack would appear in the search.
4. Less people will would have appear in a search, probably only 2 or 3 not 5. This is very very important, because more people in the game would be under a shield, than there currently is at the moment, and there is a danger of a high number of people not being available to hack. However, this is countered by the fact that people who are available should have more resources.
So basically people would be more vulnerable to be hacked and losing a lot of resources, whilst grinding out a new node upgrade. But that is countered by hacks being more profitable.
It would probably need a major rewrite and the dev's would have to review a lot of data to see just how many people would be under a shield at any one time. But hey we have a million downloads, so shouldn't be problem....
