Researchers say they recently found Google ads delivering a sophisticated tech support scam that freezes the screens of both Windows and Mac devices and displays messages urgently instructing them to phone a bogus call center.

The ads were displayed all over the web, including on high-traffic maps, weather, real-estate, document-hosting, and sports sites. Users who called the number were then urged to pay hefty fees, grant remote access to their devices, or divulge personal information. From August 31 to September 14, security firm Netskope observed users from 619 customer organizations click on the malicious ads, although none of them were actually scammed because Netskope blocked the content.

Roughly 62 percent of the organizations were based in the US, with Japan and Australia accounting for the Nos. 2 and 3 spots. Since the firm has visibility into only a tiny sliver of Internet activity, the number of people exposed to the ads—including those who fell victim to it—is likely much higher. Netskope tracked more than 250 Google Ads campaign IDs across at least 284 legitimate publisher sites.

So, what about Uncle Louie?

“For the victim, that tradecraft turns an ordinary ad click into a browser that appears to seize up on a fake security warning,” Netskope said. “The locker fills the screen, hides the cursor, swallows the usual exit keys, and lags the browser, all to manufacture the sense of a broken machine and pressure the person into calling the number on the screen. Nothing on the computer is actually locked, but in the moment it is convincing enough to push people toward the scam.”

By now, many people, including a fair number of readers of this site, ridicule and shame people who fall for such scams. These criticisms fail to account for a sizable portion of Internet users who have little or no understanding of how computers and the Internet work. Combined with their need to get things done quickly and the growing difficulty of navigating the web, this lack of awareness makes a sizable portion of users prime targets. There’s little doubt that some critics have close friends and family who are among those who simply don’t know enough to be wary.