People with cancer, especially the more intractable varieties, are often desperate. And where there are desperate patients, fraudsters will follow. The Food and Drug Administration yesterday warned 25 companies and individuals, which collectively market 125 products, to stop advertising them as cancer "cures," since there's no evidence that they can cure, prevent, or treat the disease.

The products aren't necessarily new. For example, hucksters have been peddling shark cartilage and coral calcium as cure-alls for years. (The Federal Trade Commission nailed Kevin Trudeau in 2004 for promoting coral calcium and banned him from infomercials; he shifted his marketing efforts to books.) But the Internet makes it easy to market and distribute this stuff. And the problem isn't likely to go away. There's no guarantee that a company won't just close down and set up business under another name.

So despite government efforts, the burden will largely rest on consumers. How can you tell when a claim is fraudulent? The FDA offers this list of warning signs: