One bug in an SMTP server can open up the whole machine for intrusion.

Adding functionality is not just a matter of adding code.

Writing software that's safe even in the presence of bugs makes the challenge even more interesting.

For many people my software is something that you install and forget. I like to keep it that way.

In a previous life I wrote the software that controlled my physics experiments. That software had to deal with all kinds of possible failures in equipment. That is probably where I learned to rely on multiple safety nets inside and around my systems.

Coming back to the topic of computer security, the TCP Wrapper is an example of such a safety net. I wrote it when my systems were under attack by someone who appeared to walk through walls.

When I write software, I know that it will fail, either due to my own mistake, or due to some other cause.