Top security firm RSA Security revealed on Thursday that it's been the victim of an "extremely sophisticated" hack.

The company said in a note posted on its website that the intruders succeeded in stealing information related to the company's SecurID two-factor authentication products. SecurID adds an extra layer of protection to a login process by requiring users to enter a secret code number displayed on a keyfob, or in software, in addition to their password. The number is cryptographically generated and changes every 30 seconds.

"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," RSA wrote on its blog, "this information could potentially be used to reduce the effectiveness of a current two-factor authentication implementation as part of a broader attack. We are very actively communicating this situation to RSA customers and providing immediate steps for them to take to strengthen their SecurID implementations."

As of 2009, RSA counted 40 million customers carrying SecurID hardware tokens, and another 250 million using software. Its customers include government agencies.

RSA CEO Art Coviello wrote in the blog post that the company was "confident that no other ... products were impacted by this attack. It is important to note that we do not believe that either customer or employee personally identifiable information was compromised as a result of this incident."

The company also provided the information in a document filed with the Securities and Exchange Commission on Thursday, which includes a list of recommendations for customers who might be affected. See below for a list of the recommendations.

A company spokesman would not provide any details about when the hack occurred, how long it lasted or when the company had discovered it.

"We are not withholding anything that would adversely impact the security of our customer systems," said spokesman Michael Gallant. "[But] we’re working with government authorities as well so we’re not disclosing any further information besides what’s on the blog post."

RSA categorized the attack as an advanced persistent threat, or APT. APT attacks are distinctive in the kinds of data the attackers target. Unlike most intrusions that go after financial and identity data, APT attacks tend to go after source code and other intellectual property and often involve extensive work to map a company's infrastructure.

APT attacks often use zero-day vulnerabilities to breach a company and are therefore rarely detected by antivirus and intrusion programs. The intrusions are known for grabbing a foothold into a company’s network, sometimes for years, even after a company has discovered them and taken corrective measures.

Last year's hack into Google was considered an APT attack, and, like many intrusions in this category, was linked to China.

RSA, which is owned by EMC, is a leading firm and is most known for the RSA encryption algorithm used to secure e-commerce and other transactions. The company hosts the top-ranked RSA security conference every year.

Following is the list of recommendations RSA has provided to customers:

• We recommend customers increase their focus on security for social media applications and the use of those applications and websites by anyone with access to their critical networks. • We recommend customers enforce strong password and pin policies. • We recommend customers follow the rule of least privilege when assigning roles and responsibilities to security administrators. • We recommend customers re-educate employees on the importance of avoiding suspicious emails, and remind them not to provide user names or other credentials to anyone without verifying that person’s identity and authority. Employees should not comply with email or phone-based requests for credentials and should report any such attempts. • We recommend customers pay special attention to security around their active directories, making full use of their SIEM products and also implementing two-factor authentication to control access to active directories. • We recommend customers watch closely for changes in user privilege levels and access rights using security monitoring technologies such as SIEM, and consider adding more levels of manual approval for those changes. • We recommend customers harden, closely monitor, and limit remote and physical access to infrastructure that is hosting critical security software. • We recommend customers examine their help desk practices for information leakage that could help an attacker perform a social engineering attack. • We recommend customers update their security products and the operating systems hosting them with the latest patches.

Photo: RSA SecurID tokens (br2dotcom/Flickr)

See also: