Spammers went from the public Bing URL submission tool to the authenticated version, causing a backlog of URLs that needed to be processed.

Please visit Search Engine Land for the full article.

Original source: http://feeds.searchengineland.com/~r/searchengineland/~3/O-CtncosNlM/bing-resolves-backlog-with-its-webmaster-tools-url-submission-tool-306978