From the blog

Important Security Patch Released

We’ve been notified about dangerous security threat found in one of HostBill files.
Severity depends on server configuration. We cannot leave our users at risk – we take security very seriously.

Download patch from here: https://hostbillapp.com/clientarea/patches/hostbill_patch4.6.0_4324.zip (for versions 4.4.0 and UP)

Please extract this patch in main HostBill directory. It is also available in auto-update plugin.

Version 4.6.0 available in downloads section has also been patched, so if you’re using older version it’s advised to upgrade to the latest version.