More than 75,000 computer systems hacked in one of largest cyber attacks

More than 75,000 computer systems at nearly 2,500 companies in the United States and around the world have been hacked in what appears to be one of the largest and most sophisticated attacks by cyber criminals discovered to date, according to security firm NetWitness.

The attack, which began in late 2008 and was discovered last month, targeted proprietary corporate data, e-mails, credit-card transaction data and login credentials at companies in the health and technology industries in 196 countries, according to NetWitness. The attack it is significant in its scale and in its apparent demonstration that the criminal groups' sophistication in cyberattacks is approaching that of nation states such as China and Russia.

The attack also highlights the inability of the private sector -- including industries that would be expected to employ the most sophisticated cyber defenses -- to protect itself.