Drupal is a Content Management System, similar to WordPress and Joomla. On October 15th, a very dangerous vulnerability in Drupal was announced. Within hours, exploits attacking this vulnerability started to appear on the web.
Yesterday, a special follow-up Public Service Announcement was posted on the Drupal web site. From the Drupal PSA:
Automated attacks began compromising Drupal 7 websites that were not patched or updated to Drupal 7.32 within hours of the announcement of SA-CORE-2014-005 – Drupal core – SQL injection. You should proceed under the assumption that every Drupal 7 website was compromised unless updated or patched before Oct 15th, 11pm UTC, that is 7 hours after the announcement. Simply updating to Drupal 7.32 will not remove backdoors.
Anyone who runs a Drupal site should deal with this issue immediately.