Some fool has implemented their Google Analytics tracking snippet on their website with my Tracking ID meaning my GA account is receiving data that I am not interested in from a website I have no control over. Thankfully they are sending their hostname with the requests:
<script> ...standard google stuff here... ga('create', 'MY-TRACKING-ID-HERE', 'their.hostname.here'); ga('send', 'pageview'); </script>
Because they are sending their
hostname the data is filterable in custom reports but it still turns up in the standard reporting. Is there some global account setting to reject data from certain domains? I can't believe I'm the first GA user to have somebody accidentally spamming their dataset. I hope the answer is not to declare GA account bankruptcy and move on to a clean slate.
Found the answer just by clicking around the Google Analytics admin menus. Go to Admin, in the Account column (on the left) click on All Filters, click the red button labelled + NEW FILTER, select Exclude > traffic from the ISP domain > that contain, and then enter the unwanted domain:
example.com. Choose which views you want to apply it to (I chose all of them) and click Save button.
This seems to be for stopping future data being recorded. Unfortunately I can't seem to do anything about the data that has already been recorded in this account however I will update this answer if I find a way.