Updated 7:30 p.m.: news of departure of BitTorrent CEO

As an open-source technology protocol, the file-sharing system BitTorrent is going strong, representing about half the world’s Internet traffic by some measures. But the San Francisco company, BitTorrent, is showing signs of serious trouble while it tries to commercialize the technology.

Today BitTorrent informed about half its employees, or 18 people, that they were being let go, according to a person familiar with events inside the company. That is in addition to a 20 percent staff reduction in August. In addition, a co-founder, Ashwin Navin, said yesterday that he was leaving the company, although he informed the board of directors of his exit in March.

A person with knowledge of BitTorrent’s plans also said the company would soon close its BitTorrent Entertainment Network, once conceived — and covered in the press — as a rival to iTunes. The company, with its remaining 20 employees, will focus on BitTorrent DNA, a content delivery network that helps media and video game companies distribute their products cheaply over the Internet.

Update: The chief executive, Doug Walker, a Silicon Valley veteran, has also been replaced, according to a company news release.

A spokeswoman for BitTorrent had no comment.

BitTorrent is backed by Accel Venture Partners and DCM, formerly Doll Capital Management.