Vista [...] managed to record 639 unique vulnerabilities over roughly the last half year [...] Windows 2000 [...] experienced 586 over the same period. Windows XP [...] had 1,021, with Windows 2003 Server reaching 478.
What does this data mean? You have to take the total number of users of each OS into account, as well as the age of the OS (if Vista is roughly as secure as 2000 is now, maybe that's significantly different from being roughly as secure as 2000 has a reputation for having been, when it was popular.) The article also mentions that these numbers don't take the severity of the vulnerabilities into account, or even whether they were OS vulnerabilities or just application vulnerabilities.
The Australian security company collected statistics on the number of infections by analysing figures from anonymous users of its ThreatFire community, with vulnerabilities double-confirmed by third-party anti-virus engines. The numbers are per 1,000 machines on each platform.
This makes the numbers sound more relevant, but, wow, high! Wait, 1021 vulnerabilities per 1000 Windows XP machines? That could be true -- XP is the most attractive target right now -- but it sure sounds like a lot.
Which brings up another point: there's a difference between "insecure", as in, inherently vulnerable, and "often exploited". The biggest reason why so many exploits and viruses exist for modern (NT-based) Windows OSes is that those OSes are so widely deployed, and are managed by so many inexpert users.
That's like comparing cars with horse buggies and saying cars are less safe because there are more accidents now.
What happened to growth in users, usage, connectivity, profitability of exploits, etc?