Yahoo Sitemaps are excellent to know the number of external and internal links a website has. Yahoo Sitemaps is similar to Google’s Webmaster Tools.
Recently, Sitemap users have reported that Yahoo counts https://www.example.com URLs along with regular http://www.example.com URLs. As a result, the URLs are duplicated and the sites are being penalized.
In certain cases, URLs without www are counted. Hence, http://www.example.com and http://example.com are considered as two URLs.
Resolution:
To resolve this issue,
1. Always use canonical URLs and avoid using page name URLs.
2. Use proper server side URL redirects
3. Block all secure pages using proper tags in robots.txt file