From a couple of days ago: https://news.ycombinator.com/item?id=16138708

Those antivirus companies patching early windows kernel calls to do their thing sounds pretty horrendous today, but on the other hand, at the time, they made a bad situation better (suing microsoft later was just ridiculous though).

But I think this is point in case why both the SimCity example in this article is flawed. Malloc on DOS behaved that way. Windows 95 kernel calls were patchable. If they couldn't "rely on behavior which is not guaranteed to hold in all future versions", had any of this software seen the light of day?