Assuming windows and winzip (though it may be true for other setups also).

This happens if extracting an directory hierarchy archive that contains several files files of the same name and the (WinZip) "Use Folder Names" button isnt checked.

The identical file names are supposed to go into different directories.

Example: if expanding an complex unix application you usually get a couple of hundred 'readme' ... one for each directory.

You can also check "overwrite existing files" but then you better know what you are doing.

A safe precaution is to expand into an empty directory first to check it out before extracting to a more sensitive location (Window/system ...:-).