Earlier this week, Amazon shut down one of its most popular ad units, the pay-per-click product ads that display links and images at the bottom of search results, diverting traffic out to other sites.

The reasoning behind this decision was initially unclear, but it now appears as if Amazon made the decision to shutter the ads to stop companies like Google getting access to data on Amazon users.

The product ads were especially popular with other eCommerce brands because the format enabled them to partner with Amazon without the retail giant gaining access to their transaction data. However, ad sellers like Google were able to use the ads to get information on Amazon users and improve their own ad targeting.

Amazon has shut off that valve, which was letting hundreds of companies steal from its online ad share. From now onwards, brands that wish to advertise products on Amazon will be pushed towards selling their products through Amazon as well as their own sites.

Amazon is also testing text ads that will still link out to external sites, but these are likely to be intentionally less likely to capture users attention and are more of a peace offering to those brands angry that it has closed down the product ads.