LWN.net posts a Debian security advisory message for PHP4. "It is possible to specify PHP directives on a
per-directory basis which leads to a remote attacker crafting an HTTP
request that would cause the next page to be served with the wrong
values for these directives. Also even if PHP is installed, it can be
activated and deactivated on a per-directory or per-virtual host basis
using the "engine=on" or "engine=off" directive."
January 25, 2001