Hi In three browser families researched (Edge, Internet Explorer and Firefox - all on Windows 7 or above), it is possible to extract the frequency of the Windows performance counter, using standard HTML and Javascript. With the Windows performance counter frequency, it is possible to remotely detect some virtual machines and to coarse-grain fingerprint physical machines. The full advisory is here: http://www.securitygalore.com/site3/vmd1-advisory A demo page for this advisory is here: http://www.securitygalore.com/files/vmd1.html A fix is available in Firefox 41: https://www.mozilla.org/en-US/security/advisories/mfsa2015-114/ Finally, you may be interested in my page dedicated to web-based VM detection methods: http://www.securitygalore.com/site3/web_based_vm_detection Thanks, -Amit http://www.securitygalore.com/