On multiple systems, with more or less standard make.conf values, I have found that xscreensaver (or XFree86 I suppose) is not trapping <Alt><Ctrl><Backspace> and hence does not provide the expected security. IT drops me into whatever user's console started X and I now get the account. Reproducible: Always Steps to Reproduce: 1. simply hit <Alt><Ctrl><Backspace> Actual Results: console access Expected Results: Screen should remain locked. Severity is normal or extrememly severe, based on your point of view I suppose.
*** Bug 33531 has been marked as a duplicate of this bug. ***
This isn't a bug. This is the way things are supposed to work. If you don't want people to get to the shell behind X, exec is the answer. If you don't want the X server to exit with C-A-Backspace, NoZap is the answer. Reading the docs on xscreensaver would be helpful for you. This FAQ, in particular: http://www.jwz.org/xscreensaver/faq.html#no-ctl-alt-bs