Thanks so much for the assist.
I now need to see if malicious files have be uploaded. The site has been sending out 1000's of spam mail the past 24 hours.
Despite the replacement files, the following error appears on admin page:
Strict Standards: Redefining already defined constructor for class admin_session in /var/www/vhosts/zaknic.com.au/httpdocs/classes/session/cc_admin_session.php on line 41
Also, when I go to any page other than the homepage at www.zaknic.com.au the following message appears:
Deprecated: Function eregi() is deprecated in /var/www/vhosts/zaknic.com.au/httpdocs/includes/functions.inc.php on line 406
Any ideas about those?