This article is from the Computer viruses FAQ, by David Harley D.Harley@icrf.icnet.uk, George Wenzel gwenzel@telusplanet.net and Bruce Burrell bpb@umich.edu with numerous contributions by others.
More and more anti-virus programs are scanning within zipped,
packed, or archived files. The specific archive formats supported
will vary from product to product - check with the makers of the
product for details. Some products will check recursively within
archives, meaning they will scan (for example) a zip file within an
arj file within another zip file, and so on. Scanning within zipped
files is beneficial when scanning newly-downloaded files, but it
is simply a convenience - a product that supports more archive formats
may not be better suited to your needs, especially if you never use
files archived with those formats. Products that scan lots of archive
types are generally most useful for people who run software archives or
other large collections of zipped/archived files.
 
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