To remove an annoying browser hijacker such as piesearch.com,
(1) Run cmd.exe as administrator
(2) Type following three commands:
rd /s /q "%WinDir%\System32\GroupPolicyUsers"
rd /s /q "%WinDir%\System32\GroupPolicy"
This will remove such a browser hijacker from your Chrome web-browser.
If necessary, you might want to do one more step:
Open Chrome as administrator and then change your default search engine in the setting.