Windows 8 update KB2821895 has broken down “sfc /scannow” functionality of the operating system. “After this update “sfc /scannow” gets stuck at 100% for about 6-7 minutes, and afterwards reports that there are corrupted files that it cannot fix and asks for reboot. The situation with “sfc/scannow” repeats after restart. I checked it with three different machines. There are a lot of errors in CBS.log file,” one user explained in a post. There are a lot of posts on Microsoft’s support forums about this bug caused by KB2821895 update.
A Microsoft support engineer replied to the bug report, saying that the company is now looking into the issue. “We’re aware of an issue impacting some Windows 8 customers trying to run the sfc /scannow command after installing KB2821895, where customers using the System File Checker receive an error message that there are corrupt files and that the system requires a restart to repair the files,” he wrote.
Microsoft recommends users to launch a command prompt window with administrator privileges and input the following command:
dism /online /cleanup-image /restorehealth
Then try to run sfc /scannow again until the command completes and reports that there is no corruption. If you still get an error that there is corruption, you should contact technical support for further assistance as your system may have actual corruption,” he noted.