Tobacco companies, which for years conspired to hide the health risks of smoking, are attempting to rewrite history by claiming in liability lawsuits that smokers knew or should have known that the habit was deadly, according to a Stanford history professor.

"The tobacco industry is now trying to win their cases by rewriting history, saying that everyone knew but no one had proof," said Stanford's Robert N. Proctor. "What they're saying is that everyone always knew it was bad for you. So if you started smoking in 1962 or 1972 and later got lung cancer, you have only yourself to blame."

During the same period of time, however, the industry was conducting a campaign of deception about the health risks of smoking, going so far as to declare in 1969, "Doubt is our product." Meanwhile, however, most scientists had agreed by the mid-1950s that smoking caused lung cancer.

The industry that actively sought to muddy the waters on smoking dangers is now claiming that smokers should have known the truth because of the Surgeon General's warnings on cigarette packs. Tobacco companies also claim that the scientific proof of the link between smoking and cancer only came recently.

"But if they were lying and if people actually believed their lies, then the industry can be held liable because they were manufacturing a defective and fraudulent product," said Proctor. "Millions of people in the '60s, '70s and '80s didn't know that tobacco caused lung cancer or heart disease. An increasing number knew, but not everyone knew. And not everyone knew because the industry was manufacturing doubt, fomenting ignorance. Industry executives created a climate of untruth that people bought into and died from."