On February 24th 2016 it was official. Drupal 6 was no longer supported by the community. There will be no more official security advisories or patches. The community will no longer be creating new projects, fixing bugs in existing projects and writing documentation. Essentially you could become vulnerable to anything newly discovered in D6 core or its modules. Upgrading will largely depend on how complex your site is, what contrib modules are needed and other factors.
Drupal custom development and hosting
To those running Drupal 6, there are several options available. The first options is to upgrade to either Drupal 7 or 8. The second option is to migrate away, to an CMS such as WordPress for example. If you’re considering upgrading your version, it may be wise to think about D7 at this time. It may be the more efficient option as an upgrade to D8 may require more time. Also D7 is well supported and quite stable at this time. In terms of migrating away to another CMS for example. That will really depend on how complex and customized your website is. It could make the migration tougher.
It was interesting to note as well that the majority of Drupal site owners running version 6 had never upgraded over. Even with all the warnings in the years past. There are a considerable of D6 sites still running out there. Devradius specializes on Drupal upgrades and we can always provide rough estimates on how long such a project may take. In addition to Drupal upgrades, if anyone is looking to migrate away, we can assist with that as well.