As we all know that an outdated Timthumb Plugin/extension used by many themes for wordpress are easy for Hackers to inject malicious codes. Network theme is a great theme but the Timthumb.php is not UPADTED
and its easy for hackers to hack any site using that particular theme with an outdated Timthumb.php
here is the URL
Please Update it.
I am using a great plugin to secure and hack free my wordpress here is the link of that plugin
This plugin showed that the timthumb on Network Theme is out of date.
Note: I am using the latest version of wp 3.4.1 and all the latest plugins/themes
May be I helped.. !!
Thanks and Regards