"Programmers are always looking for ways to not write code and instead use what already exists, so they all look at open-source repositories whenever possible," he said.

"They are pretty careful, but it's not easy to be sure if the license on that particular module is clean."

Microsoft indemnifies its customers against challenges to its software, and other companies sell insurance to protect users against lawsuits.

Rosenberg uses Perforce SCM from Perforce Software to control the source code, and ProtexIP from Black Duck Software to verify that code is clean.

"With all the litigation going on, this is becoming essential," he added.