Monday was a good day for the stock market, with most investors breathing a big sigh of relief despite the devastation that Hurricane Irma caused in the Southeastern U.S. over the weekend. Irma has been downgraded to a tropical storm, but it continues to bring rain, wind, and storm surges as it moves northward. Yet because it moved west to avoid a full-on hit on Miami and other population centers, major benchmarks climbed more than 1% today.

Even with the overall positive sentiment, some stocks still suffered from bad news. Equifax (NYSE:EFX), Regeneron Pharmaceuticals (NASDAQ:REGN), and AngloGold Ashanti (NYSE:AU) were among the worst performers on the day. Below, we'll look more closely at these stocks to tell you why they did so poorly.

Equifax keeps falling

Shares of Equifax dropped 8%, adding to their losses from last week following the company's massive data breach of 143 million U.S. consumer accounts. Names, Social Security numbers, birthdates, and even some driver's license numbers were among the assets stolen by hackers, and a smaller number of people had even more extensive personal information exposed. Over the weekend, many called for greater regulation of credit reporting agencies, and it will inevitably require extensive spending for Equifax to try to repair the damage that has been done. Until more details are known, investors will have to wait to learn the full extent of Equifax's liability from the event.

Four credit cards on a table.

Image source: Getty Images.

Regeneron deals with disappointment

Regeneron Pharmaceuticals stock fell almost 6% after the drugmaker released data from trials of a candidate asthma drug. The company said that a phase 3 study of dupilumab had met two primary endpoints, including reductions in severe asthma attacks and improved lung function. However, the data on asthma attack frequencies wasn't as encouraging as earlier trials had suggested, and investors had wanted unequivocally positive results from the study in order to justify their overall optimism about Regeneron. With the company already facing competitive threats from rivals on the patent front, Regeneron investors had wanted a clearer sign of success for dupilumab going forward.

AngloGold gets tarnished

Finally, shares of AngloGold Ashanti finished down 8%. The gold mining stock suffered along with many of its peers on a poor day for the gold market, with bullion prices falling $20 per ounce to $1,327. AngloGold has struggled this year after a strong 2016, which featured improved cash flow figures and a stronger balance sheet. The company has done a reasonably good job of controlling costs, but its all-in sustaining cost figures are high enough that changes in gold prices have a fairly extensive impact on its overall profitability. AngloGold needs the longer-term favorable trend in gold to continue in order to see its stock perform as well as possible.

Dan Caplinger has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.