Most of these are a failure of technology of which virus scanners are the most obvious symptom. Why is it that if I run a program on my computer it can do basic

Most of these are a failure of technology of which virus scanners are the most obvious symptom. Why is it that if I run a program on my computer it can do basically anything I can do? It can delete my files and depending on your OS all files. It can run a keylogger. It can add toolbars to my browser. It can send emails from my email account. It can access the saved passwords in my browser. This doesn't have to be the case. OSes should have been designed so that it is safe to run any program, unless you explicitly grant it permission to e.g. delete your files. If I open foo.png in an image editor, the editor should only have access to that file and the image editor's directory, not the entire filesystem. Nor should it be able to add a program to run at startup or to observe the things I'm typing in the password box of my online banking login form. Facebook at least got this partially right. When you run an application it asks you "Application X wants permission to: access your phone number, send messages on your behalf, etc.".