Does anyone know what this is all about?

In my Webalyzer log, I have all these visitors with 0 visits, especially in this particular month shown here (July 08). Most months have a FEW, but here there are a ton.

http://img186.imageshack.us/my.php?image=79659769pj2.jpg

Looks like a combo of the duration and the type of file being requested. I'm guessing a bot of some type.

Visits

  Whenever a request is made to the server from a given IP address
(site), the amount of time since a previous request by the address
is calculated (if any).  If the time difference is greater than a
pre-configured 'visit timeout' value (or has never made a request before),
it is considered a 'new visit', and this total is incremented (both
for the site, and the IP address).  The default timeout value is 30
minutes (can be changed), so if a user visits your site at 1:00 in
the afternoon, and then returns at 3:00, two visits would be registered.
Note: in the 'Top Sites' table, the visits total should be discounted
on 'Grouped' records, and thought of as the "Minimum number of visits"
that came from that grouping instead.  Note: Visits only occur on
PageType requests, that is, for any request whose URL is one of the
'page' types defined with the PageType and PagePrefix option, and not
excluded by the OmitPage option.  Due to the limitation of the HTTP
protocol, log rotations and other factors, this number should not be
taken as absolutely accurate,  rather, it should be considered a pretty
close "guess".