The Securities and Exchange Commission has opened an informal investigation into stock sales by Countrywide Financial Corp.’s chief executive officer, deepening problems at the nation’s largest mortgage lender, according to people familiar with the matter, the Wall Street Journal reports.

Countrywide is one of a dozen companies the SEC is investigating in connection with the subprime fall-out. At least one area of inquiry, these people say, involve sales by founder and Chief Executive Officer Angelo Mozilo, who sold at least $130.6 million in company stock in the first half of the year through executive sales plans.

Countrywide isn’t the only mortgage lender under investigation. New Century Financial Corp., a mortgage lender that filed for bankruptcy court protection earlier this year, is also the subject of a SEC and Justice Department investigation into accounting and stock-sales by senior executives also using executive sales plans.

These plans, known as “10b5-1” plans, have been employed by hundreds of executives to enable senior executives to sell shares at regular intervals. If executives pledge they don’t have any insider information at the time the plans are established it can be used as a defense against insider-trading charges.

Read the full Wall Street Journal story

.(subscription required)