Click fraud in online advertising is nothing new, but this news.com article triggered an interesting thought. Everybody gets all hot and bothered about "formal" click fraud, where someone clicks on advertisements over and over again to artificially drive up ad revenue. 

But what about the possibility of "informal" click fraud?

For example, when you read a blog article you particularly enjoy, have you ever been tempted to click on one of the ads as a way of leaving a tip for the author?

I'm not advocating that anyone do this, but I wonder if it happens anyway?

In the days B.A. (Before AdSense), blogs would sometimes have a "tip jar" link where you could send a buck or two via PayPal. Now you see the inlined ads instead. Paid advertising has effectively replaced the tip jar as a way to cover the costs of running a blog.

Most ads only pay a couple cents to the blog, but some can pay several dollars per click (the article mentions "medical billing software" as a search term which is particularly expensive). And I wonder why anyone clicks the usually-lame ads Google serves on this page (but people do).

Clicking-ads-as-tip-jar is a form of click fraud, since the advertisers are forced to pay for clicks with no chance to win any business.

But it would be a particularly insidious and hard-to-detect form of click fraud, since there's no way to tell the difference between lots of legitimate interest in the advertiser's products (and an especially effective ad placement) and hordes of people using the ad as a way to send a few cents to the author of the article.

So....Have you ever clicked an ad as a tip jar?