Microsoft Invest - Asynchronous usersync pixels

We've made a technical upgrade to the way we perform User ID Syncing with External Partners so that user syncing happens after a publisher's page has completely finished loading. This allows us to fire more usersync pixels per ad call without disrupting the user experience of visitors to the publisher's site. This change will benefit publishers by increasing spend platform-wide as usersyncing clients will have an increased match rate, allowing them to bid higher CPMs using their proprietary data on more users.

Due to details of the technical implementation (described below), tools such as ghostery may show more pixels firing on publishers' pages than before. Users who are fully synced should not see any usersync pixels loading; once they're fully synced, the Ghostery calls will stop.

To see how this works, clear your cookies and refresh the page several times. You will see a lot of pixels fire on the first two or three page loads (until you are fully synced). On subsequent page loads you shouldn't see any pixels loading.

The important takeaways are:

  1. While it may appear that there are more pixels on a publisher's site, the usersyncing process will only begin after the entire web page has finished loading.
  2. The queue of available usersync pixels will run out quickly (and pixels will stop loading).
  3. There should be no increase in publisher page load times - in fact, with this change page load times should slightly improve.

How it works

We attach a bit of JavaScript code to the publisher's page that will only run after the rest of the page's content has been loaded by the browser. Once a web page (or iFrame) has finished loading, this code calls our server asking for a usersync pixel. When that pixel returns and is loaded, the Javascript calls back to Microsoft Advertising again, asking for another usersync pixel. For any given tag this loop repeats a maximum of ten times, and usersyncing will stop once there are no more usersync pixels available or the queue of available pixels is exhausted. After the loop finishes, the user should be fully synced across Microsoft Advertising and all of our external partners.

For those interested in more technical details, we are appending a JavaScript callback to the browser's window.onload event. For more information about how the onload event works, see Mozilla's DOM Reference.

The steps shown below provide a simplified description of this process:

  1. Parse the HTML page.
  2. Build a DOM Tree (Browser's internal representation of the page).
  3. window.onload event occurs (DOM has finished loading all page elements).
  4. Our JavaScript code asks Microsoft Advertising for usersync pixels to load.
  5. Microsoft Advertising returns the usersync pixel to the page.
  6. The usersync pixel loads and the user ID is now synced.
  7. Steps 4-6 are repeated until the user is fully synced or 10 pixels load, whatever comes sooner.

For more detailed information about how browsers load web pages, see How Browsers Work.

European ad inventory and providing notice, transparency and choice

In order for our clients to meet their transparency, notice and choice/consent requirements under the GDPR and the existing ePrivacy Directive, Microsoft Advertising supports the IAB Europe Transparency & Consent Framework (the "Framework"). This is a reference for publishers using the macros to surface notice, transparency and choice to end users located in the EEA and signal approved vendors and, where necessary, pass consent, to Microsoft Advertising and demand sources and their vendors through the Microsoft Advertising platform. This resource should not be construed as legal advice and Microsoft Advertising makes no guarantees about compliance with any law or regulation. Please note that because every company and its collection, use, and storage of personal data is different, you should also seek independent legal advice relating to obligations under European regulations, including the GDPR and the existing ePrivacy Directive. Only a lawyer can provide you with legal advice specifically tailored to your situation. Nothing in this guide is intended to provide you with, or should be used as a substitute for, legal advice tailored to your business. Note our Service Policies (login required) (for Buying, Selling, and Data Providers) include privacy-specific obligations of which you should be aware.


Designates whether GDPR regulations are applied. Specifically, it indicates whether the user is located in a GDPR impacted country, or if we have a GDPR-required signal passed with the request. 1 if yes and 0 if no.

A "0" may be received from an EEA country. It is the publisher's choice to signal in this manner.


This is the IAB GDPR consent string. If the GDPR applies, then this will have a list of user approved vendors based on the IAB GDPR Transparency and Consent Framework.