For Security Reasons, the Library of Congress has begun filtering (blocking) HTTP requests that do not express a userAgent  in the header.


Regular human access with a standard browser is not affected by this, because browsers attach a userAgent, telling the site the sort of software being used to make the request.


However, some other services that do XML validation or access web resources without using a browser, may have problems accessing the content.

We know this is an issue and have worked to solve it for the XML standards we maintain, but there may be some stray files referenced by other schemas that continue to get blocked if a system tries to access that file without a userAgent.

There are two things to do if you have a problem with a blocked file.

1)      Report the issue to us.

2)      Where possible,  update the application you are using, to include a userAgent.




Sally H. McCallum

Chief, Network Development and MARC Standards Office

Library of Congress, 101 Independence Ave., SE

Washington, DC 20540  USA

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Tel: 1-202-707-5119 – Fax 1-202-707-0115