Criminals use cell phones. And because police agencies know this, they tend to be a little more cautious about said phones than regular users. Cautious enough to, say, buy a special fully-encrypted phone that purports to be 100% untraceable, and use the completely hack-proof messaging app contained within. Some of those criminals came to regret it as they discovered their super-secret phones and messaging service were, in fact, provided by the United States Federal Bureau of Investigation and other police forces around the world.
Vice got their hands on one of these "Anom" phones, presumably one of the ones that wasn't caught up in the international arrest stings earlier this year. They purchased it from a user who'd bought the phone secondhand online, only to do a little digging and be slightly terrified when they realized they were in possession of a device specifically designed to ensnare and capture criminals. Vice contacted the buyer, bought the phone, and poked around to satiate the curiosity of nosy normals.
This particular example of the Anom phone appears to be a Pixel 4a, probably selected because it's easy to unlock the bootloader and run custom Android ROMs. And the "Arcane OS" ROM is indeed very custom, with a layer of fake user interface pretending to be common applications. Underneath the surface UI, the phone is completely scraped of Google applications and apparently includes basic tools only. One of these is the infamous Anom chat client, which will only open after entering a specific sequence on the calculator. Other working apps include a PIN pad scrambler, making it tricky for anyone to get past the phone's login security at a glance. The software is locked down and difficult, perhaps impossible, to remove.
The "security" features are all for show. The FBI and its international partners say almost 12,000 of these "untraceable" phones were sold under the table in organized crime circles around the world, allowing them to capture millions of messages from targetted users in more than 100 countries. The Anom phones were sold from an apparently legitimate company, an ostensible competitor to boutique security vendors like Phantom Secure, complete with a service department. Confidential informers, middlemen who supplied electronics to cartels and other criminal enterprises, were convinced to slip the "secure" Anom phones to strategically important members of crime syndicates as a new and improved tool of the trade.
When the operation was completed, more than 800 arrests were made in the US, Europe, and Australia, mostly focusing on international drug trafficking. That leaves thousands of these Anom phones out in the wild, and they've now started to appear on secondary markets, often at rock-bottom prices as their users are presumably desperate to get rid of them. If you see one, you might think twice about picking it up. If you're just curious, check out the Vice report for a more exhaustive breakdown of the phone and the sting operation that used it.