These days, nearly everybody who buys search engine ads worries about click fraud… for good reason.

Click fraud is among the easiest, most risk-free crimes to commit. Here’s one common technique: First, whip up some websites acceptable for Google, Yahoo or other pay-per-click advertisements. The ads presented on your sites will be your targets. Next, download free cloaking software, like Tor, and install it on several computers, making sure you turn off the ability to write cookies. Download (or write) a simple browser script that psuedo-randomly accesses your websites and clicks the advertising links. Then watch the cash roll in.

That’s the way amateurs do it. The Big Money is much more aggressive, deploying botnets: millions of end-user desktops that have been turned into zombies by various free-range worms. Because these computers are geographically dispersed and differ in virtually every way, well-written code renders detection of click attacks nearly impossible.

Google’s Barry Schnitt sees the issue differently. He told Email Battles:

Whether or not we show ads on a query is more a question of targeting, and whether or not we charge the advertiser is the real click fraud issue.

Google has access to one of the largest sets of relevant data available, which is analyzed by an accomplished technical team using sophisticated technology to develop signals and filters to identify and filter invalid clicks.

The resulting systems strive to automatically distinguish between valid and invalid clicks, enabling us to detect and discard by far the largest percentage of invalid clicks before they impact advertiser budgets. We constantly maintain and enhance these systems, to proactively address new invalid click attack methods. and that goes on behind the scenes.

In other words, “Trust us.”

Fair enough. And that assurance is good enough for many. But the Doubting Thomases among us need more.

Companies with larger staffs, budgets and the inclination to use pay-per-click advertising, pour over web server logs, painstakingly reconciling them with pay-per-click reports from search engines, then reporting discrepancies to the providers for account adjustments. Smaller companies often simply complain more and advertise less than they otherwise might.

As in all matters human, there’s another route you can take without too much trouble.

Google advertisers can limit losses from fraud by building a high-bid campaign for ads destined for Google search engine presentation, and a low-bid campaign for ads placed in the riskier Google content network. (fyi: Email Battles participates as a member of Google’s content network. The ads surrounding this page are examples of content network ads.)

Most observers agree that the content network is where most of the pay-per-click fraud happens, as the sites that contain the advertising may be unleashed by individuals or groups with more larceny in their hearts than you’d expect from Google itself. As the content network represents a greater risk, you may want to avoid it, or at the very least, bid lower.

In fact, bidding low will keep you out of target range for most click frauders. Why waste time on a dollar bid when the world is overflowing with vastly more lucrative ten dollar bids?

In the interest of public education, Email Battles went further. As an AdWords advertiser, we simply shut down a narrowly focused business-to-business search engine campaign covering a single product for a month, then monitored both inquiries and sales results.

After thirty days of cold turkey, site traffic and first-contact inquiries were roughly the same as before. But customer follow-up and sales of those items were down a whopping 71%. Our conclusion: AdWords was delivering much more highly qualified traffic than that returned by free search engines.

So is dealing with pay-per-click fraud worth the risk? Retailers deal with shoplifters, banks fend off embezzlers, and credit card companies fight all manner of thief.

Eventually, third-party circulation auditors like Audit Bureau of Circulations and BPA Worldwide may gin up a way to provide the same level of confidence for search engine advertising they now offer for newspapers, magazines and webzines.

Until then, it all comes down to Return On Investment. If yours is good after paying the bills, it was worth it.