This is the sort of report that likely keeps a few people at the GooglePlex awake nights:

Internet advertisers paid $800 million for bogus clicks on their marketing messages last year, shaking confidence in the industry and prompting many to reduce spending with Google, Yahoo and other Web sites, according to a study to be released today.

While that's a big number, what really matters is how big it is in relation to all ad spending. Some of that context comes further down:

In today's report, advertisers say that 14.6 percent of all clicks are bogus. Moreover, three-quarters of advertisers said they had been victims at least once.

Which still doesn't tell me how big the space is. It may not matter though - the perception is what matters, and this story plays that up:

The study found that 27 percent of advertisers reduced or stopped spending on click-based advertising. An additional 10 percent said they intend to curtail spending.

"In our opinion, it is not acceptable that advertisers fund the illicit profits of the scammers," Chuck Richard, vice president of Outsell, said in the report. He added that the fraud is easy to get away with and that Web sites have done little to stop it.

I have no idea how accurate that survey is, but 27 percent is a decent size number. I've been wondering if/when click fraud would impact Google, and we might be getting near that point.