In the prior art of computer security by default programs are allowed to do whatever they like to other programs or to their data files or to critical files of the operating system, which is as absurd as letting a guest in a hotel bother other guests as he pleases, steal their property or copy it or destroy it, or have free access to the hotel's management resources. The present concept is based on automatic segregation between programs. This is preferably done by creating automatically an unlimited number of Virtual Environments (VEs) with virtual sharing of resources, so that the programs in each VE think that they are alone on the computer, and (unless explicitly allowed by the user) any changes that they think they made in virtually shared resources are in reality only made in their own VE, while the user preferably has an integrated view of the computer.