Stocks extended their slide today, giving the tech-dominated Nasdaq composite index its worst weekly performance in 17 months.

The US government has set a deadline of August 14 for many of the nation’s largest companies to submit sworn statements from their chief executive and chief financial officers guaranteeing the accuracy of recent financial reports, in an unprecedented move to help restore investor confidence.

Wall Street close mixed tonight amid concern about weak sales predictions and accounting investigations in the telecommunications and technology sectors.