HONG KONG — It was heralded as the first concrete step taken by the United States and China on the thorny issue of online espionage.

With President Xi Jinping of China beside him at a news conference in the White House Rose Garden last month, President Obama said the two had come to an agreement that China and the United States would refrain from attacks aimed at pilfering company intellectual property or trade secrets for commercial advantage.

Less than a day after that announcement and after Mr. Xi had met in Seattle with the executives of leading American technology companies, a hacking group accused of having links to the Chinese government attacked one such company, looking for trade secrets.

In a blog post on Monday, the security services provider CrowdStrike, based in Irvine, Calif., said that it had tracked a number of attacks on American tech and pharmaceutical companies leading up to and after Mr. Xi’s visit to the United States last month. (Mr. Xi has been logging airtime, making his first state visit to Britain this week.)