It's as if a robber were to break into a bank today and stay there until Christmas before someone noticed. That's how long hackers had access to JPMorgan Chase's computer system.

If two months seems like an eternity for cyberthieves to wander through the computers of the country's largest bank, consider that hackers have had free rein for even longer at several major retailers this past year. Hackers resided on the computers of Neiman Marcus for five months, Home Depot for five months, arts and crafts store Michaels for eight months and Goodwill, the thrift store, for a year and a half.