Suggested packers extension list on the providers
Scan files on open:
BAT,CHM,CMD,COM,CPL,CRT,DLL,EXE,HTA,HTM*,INF,INS,ISP,JS,JSE,LNK,MSC,MSG,MSI,OCX,PIF,PIF,REG,SCR,SCT,SHB,SHS,SYS,VBE,VBS,WS?,WSC,WSF,WSH
Scan created/modified files:
...
Archive means compressed files such as ACE,ARC,ARJ,BZIP2,CAB,COM,ECE,EXE,GZ,GZIP,LHarc,MIME,PST,RAR,TAR,WinExec,ZIP,ZOO, etc.
If Scan archive files is set, avast! scans even the content of these files. But that means that it has to unpack these file (temporarily, of course). This unpacking process may take quite a lot of time.
Do not to put archive files into these boxes - it may have very bad impact on the system performance - not speaking of the fact that the archived files don't be detected anyway unless you enable the corresponding packers in the resident protection task (Enhanced User Interface only). The archive scanning will treat them as normal binary files and will NOT scan actual content.
Note Normal/High Sensitivity was indeed changed in avast 4.5: Normal is now as High before (only selected extensions on open and copy/modify).
High now checks all files regardless of extension (on open and copy/modify).