(I work at Sift Science) If there has been no JavaScript activity from a user who makes a transaction on your site, that is a fraud signal in its own right. (

(I work at Sift Science) If there has been no JavaScript activity from a user who makes a transaction on your site, that is a fraud signal in its own right. (You can send us events from your server in addition to adding the JS to your site, so that we know characteristics of your users' transactions that can't be gleaned from the JS. In both cases you set the user ID in the call to Sift.)