Unfortunately for investors, the message arrived after market close and left some recipients more puzzled than enlightened.
"Did I sign up for this?" one recipient asked.
Yahoo has long offered consumers personalization features aimed at giving people more control over their Web experience. Its Yahoo Messenger service has an online stock alert feature with a preset portfolio that includes Yahoo. The default settings trigger an automatic notification when any stock in the group moves more than 20 percent.
Wednesday's notification came around 1 p.m. PT--nearly 24 hours after news agencies were reporting the slide in Yahoo's shares, which began Tuesday in after-hours trading, and far too late for investors to minimize their losses by dumping the stock.
Yahoo said it doesn't comment on its stock price.