As suspected, Google is moving to secure search for clicks on paid search ads. In an announcement posted by Paul Feng, Product Management Director, AdWords on the Ads Developer Blog, the company states,

“Today, we are extending our efforts to keep search secure by removing the query from the referrer on ad clicks originating from SSL searches on Google.com. Advertisers will continue to have access to useful data to optimize and improve their campaigns and landing pages. For example, you can access detailed information in the AdWords search terms report and the Google Webmaster Tools Search Queries report.”

The search term report still “lets you see search queries that generated ad clicks along with key performance data”. The search queries report in Google Webmaster Tools will continue to show aggregate information about the top 2,000 queries that generated organic clicks.

If you’re using search query strings (the terms users typed in before clicking on an AdWords ad) for reporting, in dynamic landing pages or automated keyword generation and expansion, Google recommends the following:

For generating reports or automating keyword management with query data, we suggest using the AdWords API Search Query Performance report or the AdWords Scripts Report service.

For customizing landing pages, we suggest using the keyword that generated the ad click, rather than the query. The keyword and match type can be passed to your web server by using a ValueTrack parameter in your destination URLs.

We’ll have more analysis for you as we learn more. Marin Software commented earlier today that if the change to secure search was made for paid ads, their services along with other that rely on keyword IDs rather than search query strings, would not be disrupted.

Update: I’ve clarified above that the search terms report is not new. It was renamed awhile ago from search query performance report. To reiterate, advertisers will still have access to the search query data in AdWords.