Skype, Microsoft's online telephone and video service, said it has found and now rectifying its problems that some users were facing Monday.
"We have identified the network issue which prevented users from logging in and using Skype today," the company said in a blog post. "We're in the process of reconnecting our users, and focused on restoring full service. The issue did not affect Skype for Business users."
Earlier, Monday some users were unable to make calls because their settings show that they and their contacts are off line, even when they are logged in.
Affected users were unable to change their status, but they can use instant messaging and Skype for Web services, Skype said.
--CNBC.com contributed to this report.