Operating system fingerprinting is a technique attackers use to determine the operating system running on a target device in order to select appropriate exploits. There are active and passive fingerprinting methods, such as using tools like Nmap and Ettercap to analyze response packets or capture packets from the target. While fingerprinting risks revealing sensitive information, there are also ways to avoid it like firewalls, NAT, patching systems, and modifying banners and responses. As fingerprinting techniques advance, future attacks may become more customized to specific operating systems and services.