Critics have inflated expectations about Skype's ability to monetise its 220 million users, co-founder Niklas Zennström said in an interview about his departure from the firm.

"Some people may want to monetise faster, but the key is to figure out the right speed of monetisation," he told the Thomas Crampton blog.

"If you act too aggressively, there is a real risk that you will lose the huge active user base."

Zennström stepped down as chief executive of Skype on Monday, the same day on which eBay wrote off $1.4bn on the company it acquired in 2005 for $2.6bn. The VoIP firm had posted revenues of $90m in the most recent quarter.

EBay said at the time of the acquisition that it planned to tightly integrate the two services, allowing buyers and sellers to discuss auction items through a Skype connection at an additional fee.

The eBay write-off is a clear signal that the firm has been unable to meet the initial expectations.

Zennström argued that Skype's user growth is a better measure of success than its financials, claiming that the firm had taken market share from competing services.