“Silver Sparrow” has infected nearly 30,000 Macs worldwide—and has been dubbed a “reasonably serious threat” by researchers at Red Canary, but those same security experts say they still aren’t exactly sure what the virus plans to do.

It’s a unique threat, in that the malware runs an hourly check to a control server, seeking out new instructions. But so far, none have come. And that has experts worried, since there’s no way to know when it will spring into action.

“This malware, whatever it was, did not exhibit the behaviors that we’ve come to expect from the usual adware that so often targets MacOS systems,” Red Canary said in a blog post. “Though we haven’t observed Silver Sparrow delivering additional malicious payloads yet, its forward-looking M1 chip compatibility, global reach, relatively high infection rate, and operational maturity suggest Silver Sparrow is a reasonably serious threat, uniquely positioned to deliver a potentially impactful payload at a moment’s notice.”

As of Feb. 17, Silver Sparrow has spread to 153 countries, infecting 29,139 devices running MacOS. It’s a rarity as it contains code that runs natively on Apple’s M1 chip, which few other forms of malware have been able do.

“We have no way of knowing with certainty what payload would be distributed by the malware, if a payload has already been delivered and removed, or if the adversary has a future timeline for distribution,” said Red Canary.

Apple told enthusiast site MacRumors it had taken steps to prevent additional Macs from being infected.

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