Author Clifford Stoll, an astronomer by training, managed computers at Lawrence Berkeley National Laboratory (LBNL) in California.

Stoll eventually realized that the unauthorized user was a hacker who had acquired superuser access to the LBNL system by exploiting a vulnerability in the movemail function of the original GNU Emacs.

He watched as the hacker sought — and sometimes gained — unauthorized access to military bases around the United States, looking for files that contained words such as "nuclear" or "SDI" (Strategic Defense Initiative).

The West German post office, the Deutsche Bundespost, had authority over the phone system there, and traced the calls to a university in Bremen.

When he realized the hacker was particularly interested in the faux SDI entity, he filled the "SDInet" account (operated by an imaginary secretary named "Barbara Sherwin") with large files full of impressive-sounding bureaucratese.

The hacker's name was Markus Hess, and he had been engaged for some years in selling the results of his hacking to the Soviet Union's civilian intelligence agency, the KGB.