Today, kernel extensions must be signed with a valid Apple developer account to run. That hasn’t always been the case, but even way back in OS X 10.2, Apple was trying to make them more secure:
Mac OS X 10.2 and later has stricter security checking of kernel extensions. These files should have permissions that restrict any user other than the system software (the “root” user) from making changes to the file. If a kernel extension has less restrictive privileges, it will trigger this alert.