The incidence of click fraud has reduced to 16 percent of all clicks industrywide in the second quarter; this is down from 16.2 percent. Even though it has dropped, the figure is still a significantly high number and remains a concern for search advertising businesses along with Google, which owes much of its success to pay-per-click (PPC).
… the use of botnets to perpetrate click fraud continues to rise, reaching almost 28 percent of all fraudulent or invalid clicks, up from 25.2 percent in the second quarter. This is a very concerning trend, according to Cuthbert.
A botnet is a network of computers that have been secretly compromised by malicious hackers who use them for a variety of tasks, such as sending spam and, in this case, perpetrating click fraud.
More stats on the status of click fraud can be found here.