"Second, we measure engagement of specific events on the page (e.g. when a misspelling message is displayed, and when it is clicked). This allows us to run experiments where we can test different misspelling messages and use CTR (click through rate) to determine the message's efficacy. If you are looking at network requests, these are the ones going to the one-pixel image at improving.duckduckgo.com. These requests are anonymous and the information is used only by us to improve our products."