Most Windows updates include security and compatibility updates. The security updates close various ports in Windows that if open could allow a hacker to access the information on the computers. Compatibility updates allow Windows to work smoothly with other programs causing less of a chance there will be errors they also include information and drivers for various hardware components like printers. If Windows is not updated on a regular basis the computers are left vulnerable to hacking attempts and program and hardware compatibility issues.
Anti-Virus updates include various virus definitions that help the program to identify and remove or block numerous types of malware attacks. There are literally hundreds of new and updated viruses and malware created every month. In order for an anti-virus program to be effective it has to know what to look for to find the malicious programs which is what the updates are for. If anti-virus is not updated computers are left vulnerable to malicious programs like key loggers, root-kits, and Trojan horses. Key loggers are small programs installed on a computer by hackers looking to steal credit card and login information. The program logs all the keystrokes that are made on the computer and the hacker uses that information to gain access to personal accounts(Bank accounts, credit card accounts, etc). So it is very important for your safety and the safety of your patrons to keep anti-virus software updated to avoid these types of attacks.