If you’ve ever encountered some of Donald Trump’s rabid “alt-right” supporters on the web, you know that they really relish attacking Jewish people with anti-Semitic slurs and images. Mic.com noticed this week that some alt-right Trump fans created an incredibly creepy browser extension for Google Chrome whose purpose is to mark and track Jewish people online and make them targets of anti-Semitic harassment.

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The “Coincidence Detector” extension, which was just removed from the Chrome store by Google this week, marked Jewish journalists and reporters with an “echo” tag that consists of three parentheses on both sides of their names. So if you were using the extension and reading an article by Mic’s Cooper Fleishman, you would see his name as “Cooper (((Fleishman)))” to single him out as Jewish.

The “echo” tag is a reference to the neo-Nazi notion that “all Jewish surnames echo throughout history” — that is, they believe Jewish people are responsible for myriad conspiracies over the centuries designed to extinguish the white race.

The point of the Chrome extension, wrote one neo-Nazi on Twitter, was to expose how much influence Jews have over the media and how they’re supposedly all conspiring to bring down Trump and promote Hillary Clinton.

“With this tool you begin to see patterns, constant bias, a common theme,” he wrote. “You want it deny it, rationalize it, fine, but we see it constantly. And that plugin shows it.”

At any rate, if you’re on social media and you see a Trump fan putting multiple parentheses around someone’s name, it’s because they’re marking them as Jewish and signalling to their followers that they should be targeted for harassment.