My Google search returned following utilities to be frequently mentioned when it comes to quality free rootkit scanners for MS Windows:

KasperskyTDSSKiller: https://support.kaspersky.com/viruses/disinfection/5350#block1
Malware Bytes Anti-rootit: https://www.malwarebytes.org/antirootkit/
awsMBR rootkit scanner: http://public.avast.com/~gmerek/aswMBR.htm

Bitdefender Rootkit Remover: https://labs.bitdefender.com/projects/rootkit-remover/rootkit-remover/
McAfee Rootkit Remover: http://www.mcafee.com/ca/downloads/free-tools/rootkitremover.aspx