RSA, the security division of EMC, last week announced that it had been hit with a sophisticated cyber attack that could reduce the effectiveness of the company’s SecurID authentication service.

In an open letter to RSA customers, executive chairman Art Coviello said the company had recently “identified an extremely sophisticated cyber attack in progress being mounted against RSA.”

Coviello said he believes the attack was an Advanced Persistent Threat (APT) that resulted in the hackers extracting “certain information” from RSA’s systems.

“Some of that information is specifically related to RSA’s SecurID two-factor authentication products,” Coviello wrote. “While at this time we are confident that the information extracted does not enable a successful direct attack on any of our RSA SecurID customers, this information could potentially be used to reduce the effectiveness of a current two-factor authentication implementation as part of a broader attack.”

RSA SecurID authenticators provide users with credit-card-sized devices that display six-digit passwords for their company networks on a one-line LCD every 60 seconds. Without the right number at the right time, an employee can’t log in. In 2009, RSA launched an iPhone app for the service.

“We are very actively communicating this situation to RSA customers and providing immediate steps for them to take to strengthen their SecurID implementations,” Coviello said.

The company insisted that no other RSA products were similarly impacted, nor were any EMC products. Personally identifiable information about customers and employees was also not compromised, Coviello said.

Going forward, Coviello said RSA “will share our experiences from these attacks with our customers, partners and the rest of the security vendor ecosystem and work in concert with these organizations to develop means to better protect all of us from these growing and ever more sophisticated forms of cyber security threat.”