With this feature, new stores as well as existing stores with ‘sitemap.xml’ enabled will have access to the toolkit inside Site Explorer. Within a few hours of enabling, you’ll be able to locate your indexed pages and the links to your sites, as well as delete pages in the index or rewrite dynamic URLs. To double check if your site was auto-authenticated, take a look in the ‘Source’ column in the ‘My Sites’ page in Site Explorer.
At first glance, it seems like this may make it easier for others to “steal” your site in Site Explorer. However, you still have to authenticate your site ownership using an authentication key or a meta tag.