If you're still running Windows 7 or Windows 8.1 on your PC, your machine is currently vulnerable to a strange bug that can cause it to significantly slow down or even crash. The issue will only surface when browsing a website using a special filename for something like an image source, but Windows 10 PCs are not affected by this bug.
As Ars Technica explains, the special filename in this case is $MFT, which is used by the NTFS filesystem for a specific metadata file. As it turns out, webpages that use $MFT as a directory name will cause Windows 7 and 8.1 PC to slow down or worse, as the web browser will try to access the bad file which is handled in special ways in these version of Windows. The report notes:
If the filename is used as if it were a directory name—for example, trying to open the file c:\$MFT\123—then the NTFS driver takes out a lock on the file and never releases it. Every subsequent operation sits around waiting for the lock to be released.Forever. This blocks any and all other attempts to access the file system, and so every program will start to hang, rendering the machine unusable until it is rebooted.
The unusual bug has already been reported to Microsoft but the company has yet to say when a fix will be available. As it's not well known yet, you probably have very few chances to encounter malicious websites exploiting it to force you to reboot your PC.