Actually, use of `bug' in the general sense of a disruptive event goes back to Shakespeare! In the first edition of Samuel Johnson's dictionary one meaning of `bug' is "A frightful object; a walking spectre"; this is traced to `bugbear', a Welsh term for a variety of mythological monster which (to complete the circle) has recently been reintroduced into the popular lexicon through fantasy role-playing games.
In any case, in jargon the word almost never refers to insects.
Here is a plausible conversation that never actually happened:
"There is a bug in this ant farm!"
"What do you mean? I don't see any ants in it."
"That's the bug."
A careful discussion of the etymological issues can be found in a paper by Fred R. Shapiro, 1987, "Entomology of the Computer Bug: History and Folklore", American Speech 62(4):376-378.
[There has been a widespread myth that the original bug was moved to the Smithsonian, and an earlier version of this entry so asserted. A correspondent who thought to check discovered that the bug was not there. While investigating this in late 1990, your editor discovered that the NSWC still had the bug, but had unsuccessfully tried to get the Smithsonian to accept it — and that the present curator of their History of American Technology Museum didn't know this and agreed that it would make a worthwhile exhibit. It was moved to the Smithsonian in mid-1991, but due to space and money constraints has not yet been exhibited. Thus, the process of investigating the original-computer-bug bug fixed it in an entirely unexpected way, by making the myth true! —ESR]
:bug-compatible: /adj./ Said of a design or revision that has been badly compromised by a requirement to be compatible with {fossil}s or {misfeature}s in other programs or (esp.) previous releases of itself. "MS-DOS 2.0 used \ as a path separator to be bug-compatible with some cretin's choice of / as an option character in 1.0."
:bug-for-bug compatible: /n./ Same as {bug-compatible}, with the additional implication that much tedious effort went into ensuring that each (known) bug was replicated.
:bug-of-the-month club: /n./ [from "book-of-the-month club", a time-honored mail-order-marketing technique in the U.S.] A mythical club which users of `sendmail(1)' (the UNIX mail daemon) belong to; this was coined on the Usenet newsgroup comp.security.unix at a time when sendmail security holes, which allowed outside {cracker}s access to the system, were being uncovered at an alarming rate, forcing sysadmins to update very often. Also, more completely, `fatal security bug-of-the-month club'.