If you aren't sure about getting a webanalytics tool, read about the $10.000 refund that was paid by Yahoo Search Marketing to one of their major agency clients: "One of our clients spends about $2,500 per day on Yahoo Search Marketing. In this particular instance, the client is opted into the Yahoo Content Network and spends about 20% of their daily budget or $500 per day in content. One of our senior SEM’s was reviewing daily click activity and noticed that the account, which the previous day was funded with $10K was offline and the entire available balance depleted. After further investigation we found that two particular keywords within the content network accounted for almost the entire $10K previous day deposit in less than 12 hours (rough estimate of time).
This kind of unusual click activity created a spiral of events within the Pepperjam Search Division, which initiated an immediate internal investigation by our senior team of the cause for the activity and likelihood of click fraud."
Entire story here