The post-release XP service packs, to be precise. XP's release was a perfect storm of events: Suddenly, millions of home users receiced an OS that had dozens of networked RPC services running in the background, and received DSL modems around the same time that exposed their computer directly to the internet. A slightly suboptimal combination at a time when software firewalls were a separate product you had to buy for a hundred dollars a year, if you even knew they were a thing.