Skype estimates that about two-thirds of its users are still unable to log in after an outage caused by problems with its underlying peer-to-peer interconnection system, it said in a blog post around midday European time Thursday.
Almost 5 million users are back online, Skype said, but that's still only around 30 percent of the number it would expect to see at the time of the blog posting.
The number of logged-in users is increasing all the time, but it's not possible for Skype to predict when all users will be able to sign in and start making calls again, the company said.
Even for Europe users able to log in earlier today, some instant messages and calls went undelivered or unanswered.
Skype at one stage also disabled new downloads of its software, according to a Twitter message from a company spokesman.
Skype's initial description of the problem said many of the "supernodes" that act as directories for Skype users to find one another were taken offline by a problem affecting some versions of the Skype client.
"Our engineers are creating new 'mega-supernodes' as fast as they can, which should gradually return things to normal," the company blog post said.
Send news tips and comments to firstname.lastname@example.org