Windows XP Turns 25: The Security Lesson It Left Behind

Today, October 25, 2026, it has been 25 years since Windows XP reached stores. Anyone who owned a PC in the 2000s remembers the green Bliss hills, the blue Start menu and the activation screen. Fewer people remember that XP was also the system where Microsoft learned the hard way that a Windows machine plugged straight into the internet needs a firewall switched on out of the box.

What was Windows XP?

According to Wikipedia, XP was released to manufacturing on August 24, 2001 and reached general availability on October 25, 2001. It merged Microsoft's two lines: the consumer one, which came from Windows 95 and ended with Windows ME, and the professional one, built on the Windows NT kernel.

In practice that meant user accounts, file permissions (NTFS) and an OS that did not crash entirely on every bad driver. It also brought product activation, Microsoft's first serious attempt to limit casual piracy. It was the most stable consumer Windows to date.

Why was XP such a popular target?

Was Windows XP insecure out of the box?

In part, yes: the built-in firewall (Internet Connection Firewall) was off by default, and several network services were reachable by any machine on the internet. With broadband spreading and almost nobody using a router, the PC sat on a public IP with open ports, and that became fuel for worms.

eWeek noted, around the time of SP2, that if every XP user had turned the firewall on, they would have been protected from worms such as Nimda, Blaster and Sasser. Almost nobody did, because almost nobody knew it existed.

The pattern repeated: a flaw in a Windows service (RPC in Blaster, LSASS in Sasser) and a worm that spread from machine to machine on its own, with nobody clicking anything. Conficker brought back the same idea years later.

SP2: the 2004 turning point

Service Pack 2, released in August 2004, was devoted almost entirely to security. Per Microsoft's TechNet overview, the package bundled technologies to help computers withstand attacks from viruses and worms. The most-cited changes:

• Windows Firewall on by default, on all network interfaces
• Security Center, which warned you if the firewall, antivirus or automatic updates were off
• Pop-up blocker in Internet Explorer
• Data Execution Prevention (DEP), making it harder for a buffer overflow to run code

The backdrop was the Trustworthy Computing initiative of 2002, which changed the company's development process. XP SP2 was the first large-scale test of that change. The outcome: Windows stopped being the system that "shipped open" and became one that shipped with the basics turned on.

End of support and the zombie that would not die

According to Microsoft's lifecycle page, XP extended support ended on April 8, 2014, thirteen years after launch. After that date, no new flaw got a fix for the general public.

Yet XP kept running in ATMs, industrial machines, medical equipment and forgotten PCs in a corner. In 2017, when WannaCry used a leaked NSA exploit, Microsoft made an exception and published an emergency patch for unsupported systems too, XP included. It is a rare case, not a rule.

Can you still use Windows XP safely?

Not on the internet: with no updates for more than 12 years, every flaw found since 2014 is still open. If the equipment cannot be replaced, the minimum is isolation: no direct internet access, a separate network, USB locked down and remote access disabled.

The lessons XP left behind

• Secure default beats secure option: the firewall existed in the original XP, but switched off it protected almost no one
• Worms exploit exposed services: shrinking the attack surface (ports, services) cuts off an entire class of attack
• Unsupported software is debt: the cost of replacing it only grows, and the risk runs the whole time

If you look after Windows machines today, the modern version of this lesson is in 10 settings to make Windows 11 more secure. And to see how an aging system turns into a security hole, read the story of Zotob, the worm that took down CNN's newsroom live on air. If XP was part of your life, the share buttons in the footer help spread the memory.