I had a problem installing the tun/tap adapter for openVPN on my windows 7 machines. Windows complains about the driver not being digitally signed. I don’t care about this so I switched it off by doing this:
Hit your windows key and type cmd in the ‘Search Programs and Files Box’, now instead of just hitting ENTER, use CTRL+SHIFT ENTER to run as Administrator. Type the following into the cmd prompt and reboot.
bcdedit.exe -set loadoptions DDISABLE_INTEGRITY_CHECKS bcdedit.exe -set TESTSIGNING ON