SEATTLE — Technology companies have spent months denying they know anything about broad government spying on people who use their Internet services.

But a legal case filed this week against a former Microsoft employee shows the power these companies themselves have to snoop on their customers whenever they want to.

Microsoft accused the former employee of stealing company trade secrets in the form of software code for the Windows operating system, and leaking the software to a blogger. In an investigation, the company figured out who revealed the information by reading the emails and instant messages of the blogger on his Microsoft-operated Hotmail and message accounts.

While Microsoft’s actions appear to have been legal and within the scope of its own policies, its reading of the private online accounts of a customer without a court order was highly unusual and raises questions about its protections for customer data, privacy lawyers say.