But millions of others are creeped out by the tracking that produces those targeted ads.

If you’re in that category, Ms. Winterton recommended Ghostery, a free plug-in for most web browsers that “blocks the trackers and lists them by category,” she wrote. “Some sites have an amazing number of trackers whose only purpose is to record your behavior (sometimes across multiple sites) and pitch better advertisements.”

Careful on public Wi-Fi

Most public Wi-Fi networks — in hotels, airports, coffee shops, and so on — are eavesdroppable, even if they require a password to connect. Nearby patrons, using their phones or laptops, can easily see everything you’re sending or receiving — email and website contents, for example — using free “sniffer” programs.

You don’t have to worry about Social, WhatsApp and Apple’s iMessages, all of which encrypt your messages before they even leave your phone or laptop. Using websites whose addresses begin with https are also safe; they, too, encrypt their data before it’s sent to your browser (and vice versa).

(Caution: Even if the site’s address begins with https, the bad guys can still see which sites you visit — say, https://www.NoseHairBraiding.com. They just can’t see what you do there once you’re connected.)

The solution, as recommended by Lauren Taubman and others: a Virtual Private Network program. These phone and computer apps encrypt everything you send or receive — and, as a bonus, mask your location. Wirecutter’s favorite VPN, TunnelBear, is available for Windows, Mac, Android and iOS. It’s free for up to 500 megabytes a month, or $60 a year for up to five devices.

Use Apple

“I don’t like Apple’s phones, their operating systems, or their looks,” wrote Aaron Soice, “but the one thing Apple gets right is valuing your data security. Purely in terms of data, Apple serves you; Google serves you to the sharks.”

Apple’s privacy website reveals many examples: You don’t sign into Apple Maps or Safari (Apple’s web browser), so your searches and trips aren’t linked to you. Safari’s “don’t track me” features are turned on as the factory setting. When you buy something with Apple Pay, Apple receives no information about the item, the store, or the price.