The Apache module for PHP 4.0.0 through PHP 4.0.4, when disabled with the 'engine = off' option for a virtual host, may disable PHP for other virtual hosts, which could cause Apache to serve the source code of PHP scripts.
http://www.securityfocus.com/bid/2205
http://www.redhat.com/support/errata/RHSA-2000-136.html
http://www.linux-mandrake.com/en/security/2001/MDKSA-2001-013.php3
http://www.iss.net/security_center/static/5939.php
http://www.debian.org/security/2001/dsa-020
http://marc.info/?l=bugtraq&m=97957961212852
http://distro.conectiva.com.br/atualizacoes/?id=a&anuncio=000373