Now think about this for a moment: if someone discovered and reported a security hole, CERT would issue an advisory. Most CERT security advisories focused on "exposed network services"—operating system elements that could be accessed remotely—but they also reported security holes that could be exploited by "local users," people who already had accounts on the system. The vulnerabilities were usually associated with the Unix-based operating systems–including SunOS, Solaris, Irix, Ultrix, and others—that made up most of the Internet back then.