Which setting did you use on the type page? Checking content will scan all files reguardless of extention.
From the help files
"Recognize file types by their
content.
File extensions will be ignored and the file types will be determined by their code (content). This choice is - because of the necessity to open each file and analyze its type - slower than recognizing the types by the file extensions.
name extension.
The type of the file is determined by its extension. This choice speeds up the virus scanning process.
If you select determining the file type by the content, you will have only one additional option - Scan all files. It means that even the files usually not containing viruses, e.g. text files or images, will be scanned.
If you select determining the file type by the extension, you will see the list of extensions (types) to be scanned."