Hi Kevin, Mary from Presto here. The permissions that you grant when you install the Presto Insta-Shopper app do not allow modification (or even access to) contacts, passwords or other phone settings, so it seems really unlikely that it would be our app. Also, we haven't heard any similar reports from any shoppers. What were the other apps that you installed?
Also, a reminder: if you have issues using Presto, there's a Help button right on the menu of the Presto map or in the Insta-Shopper app. That is the best way to resolve issues.