Skype service resumes after major outage

Skype is online again after a major outage that hit the majority of the internet telephony service's users.

Skype has been stabilised after engineers added extra infrastructure to the service's communications fabric, Skype's chief executive Tony Bates wrote in a blog post on Thursday night.

"At this stage we feel we have pretty much stabilised the network for the core services — IM [instant messenger], audio and video — and we're running roughly at around 90-plus percent of what we'd typically see from a user load on a day like today," Bates said in a video that accompanied the post.

Bates said the Skype service had peaked at around 20 million concurrent users online.

"The changes we've made to temporarily bring on some new supernodes appear to have worked," Bates said.

Skype's outage was caused by several of its 'supernodes' going down. A supernode functions as an addressing and data routing hub within the Skype network. There are hundreds of thousands of supernodes within Skype's network.

"In terms of root cause we now know what caused some clients, a number of clients, to crash and we've been able to mitigate that crash risk and isolate that... we also know it was not caused by a malicious attack and we're doing further post-mortem analysis on how this was caused," Bates said.

Skype will compensate affected paying subscribers in two ways. Pay as you go and pre-pay users will be sent a Skype Credit voucher via email that will yield approximately 30 minutes of free calling to landlines anywhere in the world via Skype. Subscription customers will get a week of the service for free.

The two services which are still problematic are offline IM and group video chat, Bates said, and Skype is working to bring these services back up.

The Skype outage, which began at around 4:30pm on Wednesday took down a substantial part of the network and hit both consumer and enterprise users.