June 25, 1998, and June 30, 2008, marked two important milestones in Microsoft's evolution of the Windows OS—the passing of the torch from Windows 95 to Windows 98, and the less seemly transition from XP to Vista.

In the 3,659 days between, users of Windows have been forced to bear witness to another evolution of sorts: bugs that left Windows open to exploits that appeared almost as fast as you could say, "On the Origin of Species."

[ For some fun of the hacker and admin variety, see "Stupid hacker tricks, part two: The folly of youth" and "Stupid user tricks 3: IT admin follies." ]

Uncovering—and exploiting—Windows vulnerabilities has made sport for many and careers for many more. Entire industries have sprung up to protect Windows users from previously unknown flaws, while malware authors have matured their practices from juvenile pranks to moneymaking criminal enterprises.

Caught in the middle of this never-ending onslaught is the innocent PC user and the besieged IT admin—you. And though Microsoft and the entire software industry have labored tirelessly to handle zero-day exploits and to develop protocols for reporting potential security problems, we've seen and experienced several colossal security meltdowns thanks to the humble Windows bug.

These errors, buried in millions of lines of code, have steered great corporations and turned the tide of fortunes. It's high time they got the credit they deserve. Here are the worst Windows flaws we've endured since the introduction of Windows 98.

Password "password" would have been more secure
Bug identifier: VCE-2000-0979, MS00-072
Description: Share Level Password vulnerability
Alias: Windows 9x share password bypass
Date published: Oct. 10, 2000

Windows 9x introduced a nifty little concept wherein users could host a password-protected mini file server, aka a share, on their PCs. The idea was simple: Allow users of networked computers to host and share files securely. Only the padlock Microsoft used to lock the door came equipped with a gaping hole that rendered it useless.

"When processing authentication requests for a NetBIOS share, Windows 95/98 would look at the length of the password sent by the attacker and then only compare that number of bytes to the real password," writes vulnerability expert H.D. Moore, who manages the Metasploit Framework project.

Oops. "This let the attack specify a password of zero bytes and gain access to the share," without actually knowing the password at all, Moore explains.

"The real damage," he continues, "was that by trying all characters of incrementing lengths, they could literally obtain the password for share from the server."