Welcome to Opt Out, a semi-regular column in which we help you navigate your online privacy and show you how to say no to surveillance. The last column covered what to do with your 23andMe account after the company filed bankruptcy. If you’d like to skip to a section about a particular tip, click the “Jump to” menu at the top of this article.If you’re a visa or green card holder with plans to travel to the US, reports of people being turned away at airports over messages found on their devices m...