Our developers did another build this evening, but could not wait for it to finish. Instead of locking the PC however, they turned off the monitor of the build machine whilst it was still running. This ought to have been no problem as we have a secure office, in a secure building, manned by security guards.
Upon returning home, and not receiving the automated build e-mail notification, they did a quick sanity check by remotely connecting to the build PC, only to find that the build had failed.
Upon further investigation, it turned out that the office cleaner had wiped the keyboard with a cloth, inadvertently pressing the 'space' bar causing the build to pause. The result was that the build did not complete as planned, no automated e-mail was sent and the software did not automatically upgrade our global network.
We simply un-paused the build and it completed correctly.
Not the most exciting industrial espionage or sabotage I guess we have seen, but nevertheless, a good example of the 'threat from within'.
In future, we vow to lock our PC's before we go home - honest guv!