Harvard University has sold the stock it owned in companies that manufacture tobacco products because of the dangers of smoking. The university decided to sell the stocks last September and completed the sales in March, according to Harvard President Derek Bok. He revealed the sale May 18 in a letter to three Harvard School of Public Health students, who had been demanding the university sell its investments in companies manufacturing cigarettes. ``In reaching its decision, the corporation was motivated by a desire not to be associated as a shareholder with companies engaged in significant sales of products that create a substantial and unjustified risk of harm to other human beings,'' Bok wrote. Dr. Allan Blum, a Houston physician and chairman of Doctors Ought To Care, a national anti-smoking group that pushes for divestment of tobacco stocks, called Harvard's decision a ``breakthrough morally and financially.'' ``This is a historic event that can't help but send a message that there's something rotten about holding tobacco stocks,'' Blum said. Sara Ridgway, vice president of public affairs for the Lorillard Tobacco Co., said the decision may deprive Harvard of profitable stock investments. ``I think it would behoove them to look at the best investments, and our stock has done very well,'' she said. Bok said the decision was based on an Advisory Committee on Shareholder Responsibility review. He also said tobacco companies did not adequately answer questions about ethical issues in selling tobacco and their adherence to World Health Organization guidelines for marketing tobacco products in the Third World.