In the novel “1984,” George Orwell imagined a world in which everyone was watched by Big Brother, the symbol of a brutal, totalitarian regime. It has taken another 20 years, but Big Brother has arrived. But with an irony that surely would have moved Orwell to smile, it turns out that Big Brother is us.

We still fiercely defend our privacy. The news late last year that the National Security Agency has been eavesdropping on certain telephone conversations between people in this country and foreign nationals was greeted with shock and anger, even as the White House defended the practice as necessary in a war on terrorism that knows no boundaries.

The wholesale domestic eavesdropping and personal-information gathering conducted since 9-11 under authority of the Patriot Act also has sparked a political debate over the costs of the war on terrorism in the form of lost freedoms and privacy.

An open book

But, truth be told, our lives are increasingly an open book. In the name of security and convenience we have agreed to surrender the most intimate details of our existence.

In recent decades, using increasingly sophisticated computers and advances in software, private and public agencies have been gathering mountains of personal information about us.

In many cities, police use cameras to watch the patterns of foot traffic on busy streets. Cameras elsewhere record our comings and goings at ATMs and tollbooths, and through the corridors of the buildings where we work.

They are all there to protect the collective us. But these eyes are only the tip of the iceberg. Other organizations are carefully tracking our income and spending: what we buy and how, what hotels we use, books we buy, parking tickets we receive and where we make and receive cell phone calls.

Internet “cookies” add to the information trove, as do credit-card records, credit reports, e-mail correspondence, insurance coverage, drug prescriptions and air-travel patterns.

Most of this information can be useful in nonthreatening ways. A pharmacist can use the record of your drug purchases to spot a potentially dangerous new prescription. Someone who buys only a one-way airline ticket might warrant a second look by the Transportation Security Administration. “Why isn’t he planning to return?” is a potentially ominous question.

It can be fun, if a little chilling, to have the computers at Amazon recommend books based on a previous purchase, or for your subscription to Gourmet magazine to inspire a mailbox full of cooking-supply catalogs.

If the records show you pay your bills on time, you might have an excellent credit rating even if you are deeply in debt, based on some information gathered by credit reporting bureaus.

But this convenience and serendipity comes with some dangerous hooks.

First, of course, is the menace it presents to your theoretical right not to share the details of your life with the world. You probably will pay a heavy price if you refuse to cough up much of the information that might be gathered about you.

Fail to apply for a credit card and you will discover, to your horror, that your credit rating is nonexistent when you try to buy a house.

Fail to give a prospective employer a convincingly detailed report on your college grades, income, marital status, medical history and/or hobbies and you might find your resume and application quietly set aside in favor of people willing to tell more.

Mistakes were made

Even if you see no harm in sharing, you could be in serious trouble. That’s because there is a good chance that there are errors in the information that has been gathered about you.

You might not get the mortgage or job or college scholarship if someone has made a mistake in recording your bill-paying habits. Misplaced digits on court or police documents could give you an erroneous drunken-driving record.

Not only are mistakes in records dangerously common, but there is a good chance that you will never see many important mistakes unless you request your credit records from the nation’s three largest credit rating agencies and review them carefully.

Beyond mistakes, there is the growing danger of identity theft. The Federal Trade Commission estimates that as many as 10 million Americans have their identities stolen every year. Almost everything needed to steal someone’s identity can be purchased for less than $50, experts note.

Tapping private data

Most of the technology and systems used to gather all of this personal information was developed by private companies to help marketers identify the needs and interests of consumers. After Sept. 11, an array of federal agencies including the FBI, CIA, NSA, Justice Department and Department of Homeland Security mined these databases and other sources of personal information using provisions of the Patriot Act that authorized use of previously outlawed surveillance and data-gathering efforts.

And direct government surveillance continues to move forward.

The National Security Agency, the largest U.S. intelligence agency, focuses on entire streams of communications, such as those from satellites that can carry millions of phone calls. It will intercept these in large dishes, for example, or by satellites, and then filter them through fast, powerful computers that are loaded with people’s names, telephone numbers, words, phrases … whatever they’re looking for.

Technology keeps growing

Meanwhile, technology advances, providing a growing array of potentially beneficial or dangerous pieces of information. DNA evidence can place someone at the scene of a crime or wrongfully convict them. Evidence of genetic predisposition to diseases can provide early warning of a potentially fatal condition or cost someone insurance or a job.

Experts worry that, over time, continued sweeping invasions of our privacy will fundamentally change what it means to be an American.

When we know that our movements, phone conversations, purchases and behavior are monitored, recorded and used to judge us, how can we retain the sense of personal pride and independence that defined us?

“Privacy is the right to be alone – the most comprehensive of rights, and the right most valued by civilized man.” Louis D. Brandeis