May I suggest writing a FAQ/Blog post about this ? I think more people should be made aware of this important feature and modification between 2.15 and 2.15.1.

FAQ: How do I make sure my Piwik installation add my own stats ? (Or how to prevent stats poisoning? Maybe too alarmist...)

"Since Piwik 2.15, when you add a new website or edit an old one in Administration=>Manage Websites, a checkbox under the URLs field as been added to limit which URL Piwik will accept as valid visits. When enabled, Piwik will only track internal actions when the Page URL is one of the known URLs for your website. This prevents people from spamming your analytics with URLs for other websites."

Frankly 2 years ago I was surprised it was not already there. :)

The new information from this ticket could also be added with examples to make it crystal clear for anyone. Something like :

With the checkbox enabled and these sites in the list you can expect this behavior :

URLs + checkbox enable :
http://www.example.com/
http://other.example.com

Results if one of those link to your Piwik server :
htttp://www.bad.com (Will not add any stats, that's what the checkbox is all about)
https://www.example.com (will be accounted for, Piwik don't take protocol https or http into account)
http://blah.example.com (from Piwik 2.15.1 and onward it will NOT be a valid URL for Piwik)

If my examples are bad then it means it's not clear right now! ;)

The examples are good. Now you could even do http://www.example.com/mywebsite and requests for http://www.example.com/otherwebsite would be ignored. There is already an FAQ article in http://piwik.org/faq/how-to/#faq_21077 but maybe we could add some more examples indeed and/or be more clear in the UI.

BTW: I'm not sure why I explained re subdomains but nowadays there are many services that let you for example create an account with an own subdomain or with a different path (eg ssl-account.com) that's why we let people restrict it very precisely if they want to restrict it.

I don't want to sound alarming but since the restriction for sub-domain changed between 2.15.0 and 2.15.1.should it be called a breaking change or at least be underline in the release notes as a different behavior ?

You don't want complains about stats missing after upgrading from someone expecting other.example.com to work if he had just www.examples.com and it used to work in 2.15.0.

As often the case, it's not for me, but I presume 99% Piwik "normal" users don't peruse on Github daily. ;)

We could maybe add a label "Major" which will make it appear earlier in the changelog. It might be added to the release description but this is always done when releasing the new version manually

@gaumondp thanks for suggestion, documented in the developer changelog @ 6910c97

I just read the changelog. I don't want to be picky @mattab but my understanding was that the change is not in 2.15.0 but in future 2.15.1 and it's not only important for developers but for any Piwik Super User.

@gaumondp I created #9428 so that it will show up in the user changelog as well