Login Security:Call to undefined function ctype_alnum()

After installing Login Security, I attempted to configure it in the Drupal administration screens.  I was unable to perform any configuration due to the following error.

[Wed Oct 21 11:02:53 2009] [error] [client xxx] PHP Fatal error:  Call to undefined function ctype_alnum() in /opt/sites/xxx/sites/all/modules/login_security/login_security.admin.inc on line 214, referer: http://xxx/admin/settings/login_security

In order to fix this error, you should install the "<!--StartFragment-->php5_ctype" module using your package manager of choice (i.e. apt-get, yum)