Also security expert Bruce Schneier’s October 15, 2003 edition of Crypto-Gram:

The ubiquity of the Microsoft operating system is a security
risk. There’s an inherent security risk in any monoculture, and we’re
seeing the effects of it: vulnerabilities, exploits, worms and viruses
have catastrophic effects, because they affect so many systems. How
good or bad Microsoft is at security is, in some ways, beside the
point. Because all of our OS eggs are in one basket, there’s a
significant security risk.