From the WinZip Helpfile (to me it seems like “*.'” is the right choice since %d will not add . to the path, or does avast add that itself):

Special character sequences for the Parameters field are:

. indicates where WinZip should substitute the drive, folder, and the . characters for the files that are to be scanned. For example, “c:\temp\dir*.*”.

%d indicates where WinZip should substitute the drive and folder of the files that are to be scanned. Note that the wild card characters . are NOT included when you use %d.

%f indicates where WinZip should substitute the name of a temporary “report file”. Report files should ONLY be used when running DOS virus scanners.

%wscan a special parameter required for McAfee’s WSCAN program.