A spyware researcher charges that Google and other major search engines are running ads that "push and exceed the limits of ethical and legal advertising."

Researcher Ben Edelman issued a report on pay-per-click advertising Monday, which also noted that search engines aren't liable for distributing false and deceptive ads. Under the Communications Decency Act, "Google, as a provider of an interactive computer service, may not be treated as the publisher of content others provide through that service," Edelman writes. "Even if a printed publication would face liability for printing the same ads Google shows, it appears that Google may invoke [the CDA] to distribute such ads online with impunity."

Google says it fights deceptive advertising.

"When we become aware of deceptive ads, we take them down," a Google spokesperson explained in an e-mail. "According to the Google AdWords Editorial Guidelines, 'If your ad includes a price, special discount, or 'free offer,' it must be clearly and accurately displayed on your website within 1-2 clicks of your ad's landing page.' We will review the ads referenced in this report, and remove them if they do not adhere to our guidelines."

Google's AdWords Content Policy also details at length the kinds of ads it forbids, such as pitches for spamming services, drugs, and prostitution.

But as Edelman sees it, Google isn't doing enough, despite the apparent lawfulness of its practices. "Google created this mess—by making it so easy for all companies, even scammers, to buy Internet advertising," he writes.

The ads Edelman takes issue with are offers for software that is supposedly free but isn't and pitches that attempt to deceive consumers about the identity of advertisers or products, in effect violating trademark law and Federal Trade Commission rules.

Edelman concedes that Google has been making some headway in this area by implementing systems to enforce its ad content policy, but urges the company to do more.

A likely consequence of more aggressive enforcement, however, is loss of revenue. And that's not something most companies pursue with much enthusiasm.