Historically, most modules required it, and it was distributed alongside WormKit.exe. Now that WormKit.exe is no longer in use, and various modules (such as D3D9Wnd, SuperFrontend and others I've made) no longer use madCHook, this can be a common occurrence when you install a module that depends on it.
In the past, many modules that I hosted included madCHook. Unfortunately, because it is apparently popular with malware writers, various antiviruses threat it as malware, including server-side ones hosting the files. I had to remove all traces of madCHook several years ago.