Niklas Zennstrom, co founder of internet telephony champion Skype, stepped down as CEO of the company Monday night.

Zennstrom’s departure comes as eBay wrote down the value of its Skype acquisition, admitting that it paid almost $1bn too much for the company in 2005, when it shelled out $2.6bn.

As a result, eBay said a $900m impairment charge will be written up against its third quarter results, along with a further $530m earn out payment to a number of Skype shareholders, including Zennstrom.

The earn out payments could have been as high as $1.7bn had Skype hit specific active user, revenue and gross profit targets.

Last year, it emerged that eBay was disappointed with the progress of its efforts to monetise Skype. It appears that the VoIP operator has struggled to effectively leverage its link with parent eBay and sister company PayPal to further develop its own telecoms services.

Zennstrom will remain involved in Skype as non-executive chairman. Michael van Swaaij, eBay’s chief strategy officer, will become acting CEO until a permanent successor is found.

Henry Gomez, Skype’s president, will also return to eBay as senior vice president for Corporate Affairs.

Zennstrom is expected to spend more time on his other projects. Together with fellow Skype co founder Janus Friis, he also runs P2P TV venture Joost.