what avast call Boot:Cidox-A[rtk] is called Virus:DOS/Rovnix.F by microsoft

info here
http://www.microsoft.com/security/portal/threat/encyclopedia/entry.aspx?Name=Virus:DOS/Rovnix.F#tab=2

symantec

Trojan.Cidox is a Trojan horse that modifies the NTFS boot sector's Initial Program Loader (IPL) in order to perform malicious actions.
http://www.symantec.com/security_response/writeup.jsp?docid=2011-070712-0320-99&tabid=2