All software contains bugs. Often, these bugs can result in a vulnerability that can expose your system to malicious users. Unpatched systems are a common cause of computer intrusions. You should have a plan to install security patches in a timely manner to close those vulnerabilities, so they cannot be exploited.

However if your system is not connected to the Internet the risks for attacks is rather low. OS upgrades can then be planned in sync with the recommended Product updates/upgrades.