With only normal privileges, Anthrax couldn't force the load-module program to run his backdoor Trojan program. But he could trick it into doing so. The secret was in one simple keyboard character: /.
Unix-based computer systems are a bit like the protocols of the diplomatic corps; the smallest variation can change something's meaning entirely. Hackers, too, understand the implications of subtle changes.
A Unix-based system reads the phrase:
/bin/program
very differently from:
bin program
One simple character—the `/'—makes an enormous difference. A Unix computer reads the `/' as a road sign. The first phrase tells the computer, `Follow the road to the house of the user called "bin" and when you get there, go inside and fetch the file called "program" and run it'. A blank space, however, tells the computer something quite different. In this case, Anthrax knew it told the computer to execute the command which proceeded the space. That second phrase told the machine, `Look everywhere for a program called "bin" and run it'.
Anthrax prepared for his attack on the load-module program by installing his own special program, named `bin', into a temporary storage area on System X. If he could get System X to run his program with root privileges, he too would have procured root level access to the system. When everything was in place, Anthrax forced the system to read the character `/' as a blank space. Then he ran the load-module program, and watched. When System X hunted around for a program named `bin', it quickly found Anthrax's Trojan and ran it.
The hacker savoured the moment, but he didn't pause for long. With a few swift keystrokes, he added an entry to the password file, creating a basic account for himself. He exited his connection to port 2001, circled around through another route, using the 0014 gateway, and logged into System X using his newly created account. It felt good walking in through the front door.
Once inside, Anthrax had a quick look around. The system startled him. There were only three human users. Now that was definitely odd. Most systems had hundreds of users. Even a small system might serve 30 or 40 people, and this was not a small system. He concluded that System X wasn't just some machine designed to send and receive email. It was operational. It did something.