From: utzoo!henry
Newsgroups: hacknews
Title: login(1) fixed 
Article-I.D.: utzoo.2419
Posted: Wed Aug 25 17:50:05 1982
Received: Wed Aug 25 17:50:05 1982

Figured out a way to test whether login(1) is being invoked from the
top level or not:  testing whether its parent is process #1 is not
quite 100% right, but close enough for all practical purposes.  Changed
login to refuse to cooperate if getppid() != 1.  Took the opportunity
to do some minor cleanup in the code and check usage a bit more closely.