999 Error Code on HEAD request to LinkedIn

Question

We\'re using a curl HEAD request in a PHP application to verify the validity of generic links. We check the status code just to make sure that the link the user has entered

Answer 1

It looks like they filter requests based on the user-agent:

$ curl -I --url https://www.linkedin.com/company/linkedin | grep HTTP
HTTP/1.1 999 Request denied

$ curl -A "Mozilla/5.0 (Windows; U; Windows NT 5.1; de; rv:1.9.2.3) Gecko/20100401 Firefox/3.6.3" -I --url https://www.linkedin.com/company/linkedin | grep HTTP
HTTP/1.1 200 OK