Forum Moderators: DixonJones
If you do use a persistent cookie, unique visitors will be much more accurate and will pretty much correspond to an individual machine except for error introduced by turning off or wiping out cookies.
If you use only a session cookie, look at visits, not unique visitors. Same for no cookie, though it's a lot dicier.
To see if something's hitting your site hard, look at the Visitors report, which will list individual visitors (as best as possible) and show the number of visits and page views for each. Look for either a massive number of visits for an individual visitor, or a huge ratio of page views to visits. Once you've found suspicious ones, you can backtrack to find the IP, organization, whatever.
You can do the same kind of thing with the Visiting Organizations or Visiting Domains reports - look for big visit numbers from an individual organization, or not-so-many visits but huge quantities of hits per visit.