Undetected for months, sophisticated hackers working on behalf of a foreign government were able to breach computer networks across a number of U.S. government agencies. It’s believed to be the handiwork of Russian intelligence.

And this is far from the first time.

Today, why and how such hacks keep happening and the delicate calculation that dictates how and if America retaliates.

Guest: David E. Sanger, a national security correspondent for The New York Times.

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Background reading:

• In one of the most sophisticated and perhaps largest hacks in more than five years, email systems were breached at the Treasury and Commerce Departments. Other breaches are under investigation.
• The sophistication and scope of the attack has stunned experts. About 18,000 private and government users downloaded a Russian tainted software update — a Trojan horse of sorts — that gave its hackers a foothold into victims’ systems, according to SolarWinds, the company whose software was compromised.

For more information on today’s episode, visit nytimes.com/thedaily