The stock of Minnetonka-based Digital River plunged 23 percent Monday after the company extended Microsoft's deadline for deciding whether it would renew a key distribution agreement that expires in March.

Microsoft, a software customer since 2006, was to have made its renewal decision by Dec. 1. But it now has until Dec. 19, the company said in a filing to the U.S. Securities and Exchange Commission.

Digital River, which makes software used as the checkout engine on hundreds of websites, including the online Microsoft Store, announced on Oct. 23 that Siris Capital Group would acquire the company for $840 million.

The decision to give Microsoft an extension on its distribution agreement did not please Digital River investors. Its shares fell 23 percent to $19.71 Monday. Company officials could not be reached for comment.

Sales of products for Microsoft accounted for about 32 percent of Digital River's 2013 revenues, the company has said.

The wrangling over the uncertain Microsoft Operations Digital Distribution Agreement has caused investors angst for months. On Monday, Northland Securities cut its stock outlook for the year, citing concerns that Microsoft may lower the pricing terms or decide to back out.

Digital River told investors in 2013 that it faced potential "income risks" with regard to Microsoft. It issued a warning in its 2013 annual report and in subsequent filings. In one, it said, "The termination of our e-commerce agreement with Microsoft may materially adversely affect our business, financial condition or results of operations and stock price."

Digital River posted $390 million in sales in 2013 and reported a loss of $24 million.

In the past six weeks, several law firms said they were considering filing breach-of-duty lawsuits against Digital River's board over the decision to sell to Siris Capital.

Last year, after 19 years at the helm, founder and CEO Joel Ronning left the company after several disappointing quarters. He was succeeded as CEO by David Dobson, but issues continued to dog the company.

Over two years, the company shut two data centers, sold two businesses and reduced its staff. In October, Digital River reported a smaller nine-month loss as revenues fell 5 percent compared with the previous nine months. It reported a third-quarter profit.

Dee DePass • 612-673-7725