Drupal requires cookies for user login, but by default no error message is given when a user's browser is set not to accept cookies. The result is a broken site--after attempting to log in, the user is returned to an empty login form with no indication of why login failed.
Cookie check fixes this issue. When a user submits a login form, the module checks for cookie support and provides an error message if cookies are not supported: 'It seems your browser does not accept cookies. To log into this site, you need to accept cookies from the domain @domain.' where @domain is the name of the domain the user was trying to log into.
Based on a patch by chx and others: . If you'd like this bug to be fixed in Drupal core, please test and review that issue.
There are no current plans to upgrade to Drupal 7. See.