Un-service-packed XP reachable from public would get owned in single digit minutes back in 2000s. You needed at least SP2 to slow that down. Win2K Server was

Un-service-packed XP reachable from public would get owned in single digit minutes back in 2000s. You needed at least SP2 to slow that down. Win2K Server was better, but not markedly. By contrast, a Win2K3 box with service packs and security updates could act as a server with public address if you set it up appropriately before going online. Not an accident — turns out Windows Server 2003 was their first OS to undergo extensive semi-automated bug testing with PREfast, a tool that helped catch 12% of its bugs. Additionally, human software development engineers in test (SDETs) — a claimed 60% of Microsoft's 4500 Windows devs — were crucial in finding the rest. This combined effort made it Microsoft's most rigorously tested release at the time, significantly enhancing its security.