I'm writing a novel in which an evil programmer wants to include subtle errors in his code that are likely to go unnoticed by his supervisor during a code review and unlikely to be caught by a compiler, yet cause damage at possibly random times when the program is executed by an end-user. I only need a couple of examples, which may be exotic but which have to be easily explainable to non-technical readers. Procedural or object-oriented examples would be equally helpful. (It's been a VERY long time since I've written any code.) Thanks for your help.