When anti-ICE activists rallied against the Trump administration’s deportation campaign in Minneapolis, many relied on the encrypted messaging app Signal for secure communications. In activist chats and quickly established ICE-tracking groups, locals used Signal to keep tabs on federal agents patrolling their communities.

When the Department of Homeland Security announced this week the arrest of 15 alleged “anti-ICE rioters” in Minnesota, it pointed directly at their Signal chats.

The indictment is in large part built upon on conversations from more than a dozen Signal groups, citing more than 100 specific messages. The case is a stark reminder that using an encrypted messaging platform like Signal is not in and of itself a magic bullet to safeguard communications. It also raises the question: How did Immigration and Customs Enforcement’s Homeland Security Investigations unit gain access to all of these communications in the first place?

The indictment doesn’t provide a clear answer. But sprinkled throughout the document are clues that suggest that law enforcement may have gained access to the physical devices of some of those indicted.

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The indictment singles out its targets for their alleged participation in local ICE rapid response networks, where volunteers monitor and report the presence of federal agents in their communities by flagging details such as the license plate numbers of vehicles used by immigration authorities. ICE watchers in Minnesota have been met with intimidation from immigration authorities amid the national outcry following the killings of Alex Pretti and Renee Good as they observed the actions of immigration authorities.

The 15 people named in the latest indictment are all charged with “conspiracy to impede or injure an officer,” with some facing additional charges like “solicitation to commit a crime of violence” and “destruction of government property.” Though some of the accused had court appearances on Tuesday, their defense attorneys have not as of yet been named.

The indictment comes months after FBI Director Kash Patel said in a podcast interview that federal law enforcement had started an investigation into Minnesota ICE watchers using Signal groups to share information about immigration agents.

The bulk of the indictment consists of transcripts of group messages; at various points it also makes mention of voicemails, text messages, Signal direct messages, and Signal calls. For instance, the indictment in one spot mentions that two of the indictees “exchanged approximately 20 connected Signal calls.” This hints that authorities were able to access not just group chat messages, but likely had wholesale access to the devices of at least some of those indicted.

The Signal app provides end-to-end encryption, protecting communications in transit, so that anyone monitoring your internet or cellular data connection cannot see the contents of your messages. Signal also minimizes the amount of metadata collected, so if the organization behind the app, the Signal Foundation, was served with a compulsory legal process to reveal user information, it wouldn’t even know with whom you spoke or chatted.

But all that falls apart if your device gets into the wrong hands. In order to safeguard your Signal data from someone who obtains access to your device, it’s necessary to manually harden Signal by modifying some of its default settings.

Perhaps Signal’s most well-touted security and privacy feature is its ability to set disappearing messages. Messages can be set to expire in periods ranging from seconds to weeks. A default expiration time for all messages can be selected, and specific groups and conversations can be set to custom retention times. To minimize risk, set retention times to the shortest amount feasible — minutes or hours, instead of days or weeks.

Keep in mind that Signal’s disappearing messages delete the contents of a message, but they don’t remove evidence that communications between parties occurred in the first place. This means that even if a group has enabled disappearing messages, someone who gains access to a member’s device could later determine with whom they were chatting. Therefore it’s safest to regularly delete entire groups and chats, not just the messages themselves.

Just like its chat function, Signal also has keeps similar records of voice and video calls. It’s as important to delete records of the calls as it is records of text messages, both within the Signal app and in your phone’s standard call history.

On iPhones, Signal can integrate its call history into the iPhone’s regular call history. This privacy-eroding feature can be disabled on Signal on iOS by tapping your profile circle on the top-left corner of the app, clicking on Settings, then Privacy, then disabling “Show Calls in Recents.”

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Additionally for Signal on iPhones, you’ll also likely want to disable settings like “Share Contacts with iOS” and “Use Phone Contact Photos” (for Android users, the equivalent is “Use address book photos”), which can be found under Settings, then Chats.

Such precautions may sound extreme, but in a recent case, authorities were able to recover deleted incoming Signal messages based on old push notifications that were archived on iPhones (the latest iPhone update fixes this issue, highlighting the importance of keeping your devices up to date). On that note, remember to either turn off Signal notifications entirely or have them display only the names of people sending messages — which should be pseudonyms, not real names.

The post How Did the Feds Get Into Anti-ICE Activists’ Signal Messages? appeared first on The Intercept.

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