Windows: where the security debt came from

Windows is the world’s most widespread PC operating system, but it is also historically the most exploited. Why is Windows so insecure? This is one of the most frequently asked questions in the IT field. Here, we will try to give an answer looking at how it was born and how critical design decisions created a long-standing security debt.

Three milestones are particularly relevant.

1. QDOS, IBM, and a Foundation Without Security

How Microsoft is born?

In 1981, Bill Gates acquired QDOS (Quick and Dirty Operating System) to meet IBM’s urgent demand for an operating system. QDOS was never designed with multi-user protection, memory isolation, or privilege separation in mind, it was a single-tasking, trust-based system for standalone machines.

MS-DOS, and later the first versions of Windows, inherited these weaknesses.

Windows was built on an architecture where any process could directly interact with hardware and memory.

2. Features Over Security, Winner Takes All!

In the late, Microsoft’s strategy was clear: market dominance through features.

In the IT field, the rule ‘the winner takes all’ often applies. A technology that becomes dominant, such as an operating system, naturally attracts developers who want to build applications for the most widely used platform rather than for an obscure niche one. This creates a vicious cycle that is hard to break, because users, in turn, prefer the operating system that supports the largest number of applications, making it even more popular.

Windows was first to market, and until the 2000s its policy was clear: release as many features as possible without spending time on security checks. The goal was to provide applications for every need, such as Word and Excel, and to outperform the competition.

This approach gave Microsoft massive adoption, but also created a monoculture where attackers could focus efforts on a single target and achieve global impact.

3. The Internet Rush: A New Attack Surface, Same Old Weaknesses

By the mid-1990s, the Internet had gone mainstream. Microsoft integrated TCP/IP networking and Internet Explorer into Windows at breakneck speed. Security testing was minimal.

We can say that Bill Gates did not immediately understand the Internet and its potential, and at first he even discouraged the open protocols that defined it. In the early days, PCs within companies were connected only through LANs, and going ‘online’ mostly meant accessing BBS platforms.

Instead of being modular and secure by design, Windows was a patchwork of rushed integrations. Each shortcut created opportunities for attackers.

A Different Story: Unix, Linux, and the Multics Legacy

In contrast, the Unix family, from which Linux descends, had very different roots. Unix was influenced by Multics, a project born in the 1960s that emphasized security, privilege separation, and multi-user isolation from the start. Even in its earliest versions, Unix implemented:

• User and group permissions (UID/GID) to separate access.

• Process isolation enforced by the kernel.

• File system protections with strict permission models.

  
  

Linux inherited this philosophy. Although not immune to vulnerabilities, its architecture was shaped around security by design, not retrofitted later.

That's why Linux has historically been favored in server environments, critical infrastructure, and security-sensitive contexts.

A Security Debt That Still Echoes Today

These three milestones, QDOS origins, the “features first” race, and the Internet rush explain us why Windows has historically carried so many vulnerabilities.

Even as Microsoft invests billions in modern defense strategy the burden of maintaining backward compatibility makes vulnerabilities difficult to close.