Shares of CyberDefender Corp. fell more than 13 percent on Wednesday after the struggling Internet security software company said that Gary Guseinov, chairman and chief executive, had resigned.

After the markets closed on Tuesday, the Los Angeles company said that Howard Bain, an independent board member, had been elected chairman. The board is negotiating with Greg Thomas, an adviser to the company since late May, to serve as interim chief executive.

The reason for the resignation of Guseinov was not disclosed. A company spokeswoman on Tuesday said executives were not available to comment.

CyberDefender’s stock have been steadily falling since late last year, and shares have been in danger of being delisted from the Nasdaq since falling below $1 on July 19.

Even so, the company on Tuesday reported a smaller second quarter loss on higher revenue. The net loss fell to $6.6 million, compared with a $12 million loss in the second quarter of 2010. Revenue rose 31 percent to $12.7 million.

CyberDefender, which began beefing up its tech support service last year, also announced Tuesday that it laid off part of its software development staff.

Kevin Harris, the company’s chief financial officer, said in a statement that CyberDefender will now focus on licensing security software and on the company’s LiveTech support service.

“During the second quarter, the company determined that it was the opportune time to formalize a plan which would enable us to best capitalize on our strength with direct to consumer marketing and leverage our position as a leading provider of remote technical support services,” he said.

Shares closed down 11 cents, or 13.6 percent, to 70 cents on the Nasdaq.