Prevent all subdomains from being crawled by search engine bots

I have a domain like domaindev.com.

I have set the robots.txt file on this domain to block everything:

User-agent: *
Disallow: /

Just like that. So that blocks everything from being crawled.

Now here is where it gets interesting. We also have several subdomains.domaindev.com hosted on our server and I want to block all of those subdomains as well from being crawled. I want a simple way to block any old subdomains and any new subdomains. Is there a line I can add to the www.domaindev.com that will prevent any subdomains under the domaindev.com?

Is the best way to make a default robots.txt and just drop it in all of the subdomain folders manually.

I’d really like a definite solution so as not to have to continually do same.

We use WordPress and in the wp-admin we have set it to not let spiders crawl our websites. But somehow these websites are finding there way into Google.

How do I go about it?

I’ve searched the site and found this line to add to my .htaccess file:

Header set X-Robots-Tag "noindex, nofollow"

I’m going to do that as well.

I also saw that it is part of the standard that each subdomain would need its own robots.txt file.