ProjectPHP, most of you have seen him around at the forums, tipped me off on this. At the end of a thread on click fraud that we covered about a month ago, in the entry named 50% of PPC Clicks are Fraud, we learn more.
In the 3rd page of the thread it says
Netscape's quick Searches, if they are words you bid on, can cause budgets to absolutely blow out, and fast. In your case, it was $1,000 per day. That is a massive ammount to potentially save, and a tip well worth knowing!!
I nice bit of advice to share with you.