Microsoft wrote down the value of Aquantive by $6.2bn (£3.94bn, 5bn euros) and failed to bring the profits expected.
The computing giant thus made a loss of $492m in the three months to the end of June, compared with a profit of $5.9bn a year ago.
The company had never made any loss since 1986 when it joined the stock market.Revenue for the three months to June rose by 4% to $18.06bn.
Meanwhile Microsoft has announced that its next-generation operating system tailored for a world shifting from personal computers to smartphones and tablets will be available on October 26.
Windows unit boss Steven Sinofsky revealed the Windows 8 debut date at a sales meeting, Microsoft communications manager Brandon LeBlanc said in a blog post yesterday.
Windows 8 will be available in 109 languages across 231 markets worldwide, according to LeBlanc.