For example - my referral logs are completely littered with sites such as (I am making these up but they may be real sites)
bestsearcharound.com
isearch4u.com
searchstarsite.com
and on and on all of which send between 1 and 15 visitors (most of them 1-5).
Are you guys seeing the same thing?
[sorry for the misspelling of the title, only caught the afterwards]
I just tested a product called Who's Clicking Who and it shows the majority of clicks were from an AOL proxy. Apparently this is because AOL is a really big partner with Google.
There were also a lot of repeat clicks that looked like they were just visitors that went wild with the clicks (4 or 5 clicks). Some of the others clicked a couple of times and skip a day and click a few more times, this was the activity I was looking for and found only a few.
I only advertise in the US and I use negative keywords like "India" and "Russia" to hopefully keep them from seeing my ads. If you are advertising worldwide you may have a bigger problem. Then I would recommend getting software like Who's Clicking Who for a while to see exactly what is happening.
With that in mind I set up a huge list of negative keywords (Like -keyword) and made sure "India", "Russia" and a lot of other words like "free", were among them.
When you go into your campaign you will see a place to add negative keywords or you can add them like regular keywords with a "-" in front of the word. I found out that I've been spending way too much on searches that don't pertain to what I sell. Negative keywords are used mostly for the broad match.
I also turned off the content network in the section where you edit your campaign. After doing this I noticed a huge increase in my CTR and I think it got rid of some of the click fraud. The content network is something that I will have to do more testing on later.