The link checking information is read by the VLO when importing resources and regularly updated. The VLO discards any information that is too old (more than 100 days). Resources that were found to either be unavailable or require special permissions to access are marked with an icon to indicate either unavailability (warning sign) or restricted access (lock icon). This classification happens on basis of the encountered HTTP response code (for example 404 or 503 is classified as unavailable, 401 or 403 as restricted). These icons are shown in the VLO search results for records with one or more problematic linked resources. The resources detail panel of record pages show a status per link. Each link can be expanded to reveal details regarding the last check: status code and time of checking.
Note that the link checking information may be outdated at the time it is displayed in the VLO. The link checker can only check the status of each resource location with a certain frequency, and the availability status may change.
If you find that a resource found in the VLO is actually unavailable or has restricted access but would like to access it, contact its provider via the landing page (if available) or look for contact information in the 'All metadata' tab.
If you are a resource provider and believe that the displayed accessability status information shown for your resources is incorrect, please contact the VLO developers (email@example.com).