Many sites have webalizer stats built in on shared servers. Many add their stats page to the public eye to boast their amount of visitors. This is useful because you can easily google search webalizer usage statistics and get a huge list of sites, whose stats you can look at. You can even do a keyword search for just webalizer and just go down 10-100 pages.
You can also include a keyword related to your site and find sites of your competitors. You can find what the most popular keywords they have and find ways to exploit the keywords and bring your site to the top of the list for the best keywords.
People can datamine a google search and go through all the webalizer sites collecting keyword data and most common referals. Exactly how this is done is beyond the scope of this article but it's not as complicated as it seems. Basically they can do an advanced search with 100 links listed, then parse the nongoogle links with something like preg_match_all in php. From there it's a matter of just again, collecting all links in the front webalizer page, then deleting everything above and under the keywords section.
AWstats rivals webalizer, along with smarter stats, analog stats, can all be exploited just in the same way. This really isn't a "hack" but many sites have shown using the keyword hack 1) draws more people 2) makes people feel special 3) is now used as meaning "using something differing from it's original intention".