Mysterious subdomains to my site indexed by Google

Question

We have an issue with strange subdomains pointing to (pages on) our site such as:

• www2.example.com
• 2.example.com
• anothersite.com.example.com

A few things are perplexing:

• who created them? why they do that?
• why Google index them and made them appear in the search results when clicking them gets a 5xx error.
• how can we get rid of them?

It seems some type of scams that hurt our site's free search and experience. Anyone had similar experience and knows the answers?

Answer 1

I have similar problems on some websites, if you are running apache web server you can do 301 redirect to your main domain with this code

RewriteCond %{HTTP_HOST} ^(www2|2|anothersite.com)\.(.+)$ [NC]
RewriteRule ^(.*)$ http://%2/$1 [R=301,L]

If you don't have dynamic subdomains, you can easily route all that backlinks to your main domain. And, this can't " hurt your site's" if you don't have content on these subdomins (you told that you have 5xx errors), if you have content on any of those subdomains, you can get problems with duplicated content, but it's usually easy to handle. I don't know who created that subdomains, but sometimes they created accidentally, mistyping..