Opening suspicious files
Open up the terminal and try: 

zipinfo zipFileOfInterest.zip


If you really want some "verbose" information output, then enter:

zipinfo -v zipFileOfInterest.zip


The "-v" option will output a bit more information :)

Also, try man zipinfo to get the rundown of what options/etc is available.

You can also try:

unzip -l zipFileOfInterest.zip


These will allow you to peak inside the .zip without extracting what is inside.