Entrust Technologies

(ENTU)

said Monday that John Ryan has resigned as president and chief executive, effective immediately.

Board member Alberto Yepez, the president of

Entrust New Ventures

, and David Thompson, the company's chief financial officer and executive vice president, will act as co-chief executives while Entrust looks for a permanent replacement for Ryan.

Ryan is leaving the Internet infrastructure software and products company for "a new challenge," he said in a statement.

Shares of Entrust fell 32 cents, or 2.2%, to $14.13 in regular session

Nasdaq

trading, but slipped to $12.50 in recent after-hours

Island

activity.