BleepingComputer recently reported that every computer running Windows 10 is vulnerable to having its system hacked unless the user changes the default setting for viewing files.
Every file has an extension, which are the letters shown after the name. Common file extensions include .doc, .pdf, and .mp3.
By default, Microsoft hides a file's extension. However, this is a security risk that cybercriminals often take advantage of to trick users into opening malicious files sent through phishing emails and malware distributors.
Because Windows hides the file extension, users are more likely to think that malware that has an innocent file name is safe. If the user could see that the file extension is .exe instead of .pdf, he or she might be more wary. Gordon Kelly "Warning Issued For Millions Of Microsoft Windows 10 Users" forbes.com (Mar. 03, 2020).