RadioShack, Dell, Lockheed and Cablevision are big market movers

NEW YORK — Stocks that moved substantially or traded heavily Friday on the New York Stock Exchange and the Nasdaq Stock Market:

NYSE

RadioShack Corp., down 32 cents to $2.57

The retailer's shares tumbled after Standard & Poor's said the company could default within a year and downgraded its credit rating.

Weight Watchers International Inc., down $9.04 to $37.99

Fewer people are signing up for the company's programs, which drove second-quarter net income down 16 percent. It also booked costs related to paying down debt early.

Cablevision Systems Corp., up 97 cents to $19.61

Lockheed Martin Corp., up $1.60 to $123.77

The Defense Department stressed that there are no plans to scrap the F-35 program or a project for a new long-range stealth bomber. Lockheed's F-35 is the Pentagon's most expensive weapons acquisition program, and an aircraft with a troubled testing record.

Nasdaq

Dell Inc., up 73 cents to $13.68

Dell's board agreed to an increased offer from founder Michael Dell that would add a special dividend for shareholders. Michael Dell is in a battle to buy the slumping computer maker he founded nearly 30 years ago.

The generic pharmaceutical company's stock hit an all-time high on an upgrade from Morgan Stanley. Analyst David Risinger said that Mylan had "crystallized future growth opportunities," which should increase investor confidence.

Body Central Corp., down $3.86 to $8.10

The trendy women's clothing company saw traffic at its stores decline and it was forced to make deep markdowns on its merchandise during the second quarter.

Alaska Communications Systems Group Inc., up 60 cents to $3.15