Please scan the PC that uses your cPanel account with an updated AV and Malware scanner to ensure that the infection is removed.
WordPress, Joomla, Drupal etc comes with Free Plugins and Free Themes to download. Some of these Themes and Plugins usually do Automatic Updates from the server they were downloaded from. In some cases when the scripts are not Secured, the updates are downloaded into your server with Viruses, which could include Spamming scripts and hacking scripts, which has evidently happened in your case. Sometimes these unsecured scripts are programmed to stay dormant in your account until a certain period. So it is very important to only download Secured Scripts into your CMS, be it WordPress, Joomla, Drupal, Moodle etc.
Tuesday, February 23, 2016