libapache2-mpm-itk - 2.4.7-04-2 main

The mpm-itk module, although not technically a Multi-Processing Module (MPM)
(although it used to be) enhances the classical "prefork" module (that is,
without threads), in such a way that it allows you to constrain each
individual vhost to a particular system user and group. This allows you to run
several different web sites on a single server without worrying that they will
be able to read each others' files. mpm-itk is largely independent of e.g.
what scripting technology is in use on your server; in particular, it does not
require you to run your scripts as CGI to get the extra security benefit.