Yahoo Site explorer officially closed from today
Yahoo was one of the best explorer giving you insight about incoming links to your site and has been the choice backlink discovery tool for several years. Unfortunately we have no other Free alternative to yahoo site explorer right now. But we can move to some paid tools like Majestic seo and SEO Moz.
I think main issue behind closing down is cost factor, maintaining and running this kind of project costing them much of their resources and in return giving them nothing.