Some time ago I created the domain in .com zone. Now I tried to evaluate the number of pages are in Google index using request like site:mydomain.com but surprisingly there were a lot of results like:Pools Above Ground Store poolsabovegroundstore.mydomain.com/ Intex  15-Foot-by-42-Inch Family Size Round Metal Frame Pool Set Intex  56948EB. Intex 15-Foot-by-42-Inch Family Size Round Metal Frame Pool  Set.All those links are not working giving 404 error.This domain hosted on Hostgator shared hosting. Do you have any ideas how does all of those pages appeared in Google index?
Google Search for my domain has about 3500 3-rd level subdomain I did not create
google search;links;google index
If Google indexed those links, this is because they existed in the past. Googlebot found them by following existing links on another page (internal or external).If you don't want to see those links  in Google index, you can return a 410 HTTP status by using an .htaccess file for example (if you use Apache as a web server). See this topic for this.Just for information, your web host has nothing to do with this.