Filtering out traffic that is not from your website
It sometimes happens that someone will accidentally use your GA Web Property ID (UA-xxxxx-y) in their website.
When this happens, pageviews and visits from their website will show up in your GA reports.
To prevent this, you can create a filter and apply it to your main profiles.

The screenshot shows the use of a Custom -> Include filter on the Hostname field. This example is for the site cats.com.
We are only including pageviews that happen on a domain that matches the regular expression “cats.com”. This will match all of your subdomains such as my.cats.com or pictures.cats.com.
Website spanning multiple domains:
If you have a website that spans multiple domains such as cats.com and mycats.com and bluecats.com, then instead of filtering on “cats.com” you simply list all your domains, separated by a pipe:
Instead of:
cats.com
use:
cats.com|mycats.com|bluecats.com
Note:
If you have a profile that doesn’t have any filters on it, for raw data and troubleshooting, make sure you don’t add this filter to that profile.


Thanks for sharing website spanning details with us.
I also use this filter although there is small probability of such a situation:) Another solution istead of pipe is in my opinion regular expression:]
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