Federal officials warned Tuesday that a massive Chinese hacking operation against American telecommunications companies has not yet been fully dismissed and that the best way to hide communications from Beijing’s spies is to use encryption.

Encryption is a technology that encrypts a message and requires a “key” to see or hear it.

Various app makers and platforms have been using the technology in various forms for more than a decade, so governments and hackers who intercept them passing through telecommunications infrastructure only see nonsense. While the technology’s adoption has drawn complaints from law enforcement agencies – including the FBI – in the past, it is also a way to communicate more privately.

Telecommunications companies tend to temporarily store call and SMS records – which phone number called or texted when – and briefly store the content of SMS texts. However, audio is generally not recorded. That means it’s easier for hackers like those in the Chinese campaign that Microsoft has nicknamed “Salt Typhoon” to obtain huge amounts of data on phone records and some stored text messages, but they must specifically listen in on specific phone calls when they take place .

For ordinary consumers, the easiest way to send encrypted messages or make encrypted calls is to use communication apps such as Signal or WhatsApp, which have implemented end-to-end encryption between other Signal and WhatsApp users. With end-to-end encryption, each user of an encrypted chat app has the unique code to decrypt a message sent to that account. Importantly, the business owner and app operator do not have access to this key, so they cannot decrypt an encrypted message even if a court requires it or it is hacked.

In this way, Signal and WhatsApp automatically protect all their messages with Signal’s encryption, which is among the best commercially available for cryptographers.

With both apps, users can also make encrypted calls to other users over the Internet.

But even without apps like Signal and WhatsApp, many Americans often text with end-to-end encryption enabled, even if they don’t know it.

When iMessage users text other iMessage users or Google Messages users text other Google Messages users, those chats are automatically encrypted using the Signal protocol.

However, when Google and iMessage users send text messages to users who use different SMS applications, such as when an iMessage user sends text messages to a Google Messages user, the messages are encrypted only using Rich Communications Services, all of which are available in the United States be decrypted by Google. While this means they are theoretically hidden from telecommunications companies, they are not end-to-end encrypted and can be viewed by Google under court orders or by hackers who might break into companies.

For phone calls, Google and Apple offer encryption when the calls are made through their internet-connected calling apps – Google Fi and FaceTime.

While the controversial app Telegram reportedly offers a way to send users messages with end-to-end encryption, some leading cryptographers have shied away from supporting it because some of its code is not available to the public for testing not encrypted.

The FBI began investigating the Salt Typhoon in late spring or early summer. The U.S. believes Chinese intelligence agencies hacked into AT&T, Verizon and Lumen Technologies and gained significant access, including recordings of phone calls and text messages to many people, particularly in the Washington, D.C. area. Under certain circumstances, both members of the Trump – as well as the Harris campaign and the office of Senate Majority Leader Chuck Schumer DN.Y., they were able to listen in on telephone conversations.

China denied the accusation, as it routinely does when a Western company or government accuses it of using its vast cyber espionage capabilities. A spokesman for the Chinese Embassy in Washington said in an emailed statement: “China firmly rejects the US’s slander attacks against China without any factual basis.”

This article was originally published on NBCNews.com