Johnson & Johnson said on Monday it plans to buy back up to five billion U.S. dollars of its stock, after a report that the company knew for decades that its Baby Powder contained cancer-causing asbestos wiped about 40 billion dollars from its market value.

Shares of the company closed down five percent on Monday, extending a 10 percent fall on Friday after the report was published.

They were up about one percent in extended trading following the announcement of the share buyback. The repurchase plan has no time limit and may be suspended for periods or discontinued at any time, the company said in a statement.

J&J knew about the presence of small amounts of asbestos in its products as early as 1971, an examination of company memos, internal reports and other confidential documents showed.

The share repurchase was just the latest effort the healthcare conglomerate has made to boost investor confidence.

In response to the report, the company said on Friday “any suggestion that Johnson & Johnson knew or hid information about the safety of talc is false.”

On Monday, J&J took out a full-page ad in the New York Times titled “Science. Not Sensationalism,” saying it has scientific evidence its talc is safe and beneficial to use. “If we had any reasons to believe our talc was unsafe, it would be off our shelves,” the ad said.

“We unequivocally believe that our talc, our baby powder, does not contain asbestos,” said Alex Gorsky, J&J chief executive in a clip CNBC released ahead of the interview. He also touted the company's testing practices for determining whether the talc was safe.

While J&J has dominated the talc powder market for more than 100 years, the products contributed less than 0.5 percent of its $76.5 billion revenue last year. The company has large pharmaceutical and medical device portfolios in addition to its consumer products business.

J&J shares were trading at $130.30 in after hours trading following a close at $129.14 on Monday.