If you decide to uninstall a third-party add-on, and if the module is listed in the Activities, Blocks, or Filters section in the Modules menu, you have to use the provided delete option.

The delete operation will remove all data associated with the module and display a message to confirm the success. To complete the deletion and prevent the module re-installing next time, go to the admin page and delete the directory from your server that is displayed on the screen:

The message about deleting the directory only applies to blocks, activity modules, filters, question types, authorization, enrolment plug-ins, and other modular software components. It does not apply to other types of third-party software such as hacks, patches, an d so on, which have to be removed manually.