Forrester Research estimates that 27 percent of Web users have used an ad blocking tool, a sharp increase from recent years.

It is possible to take much stronger steps, too, and Tor is one of the most popular options. Originally developed for the Navy, and used by agents for the Federal Bureau of Investigation, Tor’s browser prevents Web sites from knowing who you are by rerouting Web traffic through a series of other points. Using Tor with your e-mail service, for instance, would most likely prevent a government agency from detecting your Internet Protocol address, though not from compelling a service provider to turn over your messages.

Orbot offers an equivalent for the Android operating system; there is nothing for iOS.

A virtual private network, or VPN, can also help blur your tracks. It creates an encrypted tunnel between your computer and the VPN’s server, obscuring your Web browsing to others, including your Internet service provider. But some VPNs log your Internet traffic, compiling a rich history of your Web travels. HTTPS Everywhere, a browser extension, takes you to secure, encrypted versions of Web sites wherever possible, protecting you from eavesdroppers, for instance, when you are using public Wi-Fi.

If you do not want Google or Bing (the two main search engines) to compile your search history data, there is the upstart search engine called DuckDuckGo.

Its founder, Gabriel Weinberg, says his company has no interest in saving user search history. The company makes money by serving advertisements based on the keywords searched, right then and there, and discards the search history. So if the government asks for user information (that hasn’t happened yet, he said), it will not get much. “If the data doesn’t exist, there’s nothing to hand over,” he said.

TRUSTING THE CLOUD Lawyers sometimes like to say that the digital cloud has fundamentally changed the relationship between citizens and their governments. If the police wanted to inspect your work files in the past, a search warrant was required to enter your office. Now, the police can turn to the cloud service you use to store work files.

But when SpiderOak, of San Francisco, receives these inquiries, it cannot offer anything legible. Its customers’ files are not only encrypted, but users’ plain text passwords are not transmitted to the company.