Legitimate user credentials are the digital lifeblood of attackers looking to compromise a network. With valid credentials, attackers can infiltrate a target network, elevate their privileges to gain access to more sensitive data, and take control of critical systems.

To combat an attacker's ability to use stolen credentials, companies need to model the behavior of every user -- especially those people, such as system administrators, with access to privileged accounts. Using that baseline, businesses can detect whether the use of a credential falls outside of what is typical or allowed by policy, says Philip Lieberman, president of Lieberman Software, a privileged-account management provider.

"You have to look at not only what a person can do and who they are, but to look at their behavior and whether that behavior has become risky," Lieberman says. "Then you can respond to a high-risk score by shutting down the account if the behavior of the user is becoming anomalous."

At the Cloud Security Alliance (CSA) Congress in December, Lieberman and industry experts will discuss how authentication can be used to better secure cloud services and network infrastructure from attack. The fundamental problem is that few companies have a good idea of how many privileged-user credentials are in existence, where they are stored, and whether an account is still necessary for business, he says.

Companies typically have three or four privileged accounts per employee, most which are not monitored or managed by the business, according to a recent survey by CyberArk, a privileged-account security firm. Finding those accounts and monitoring their access is critical to heading off insider attacks and more persistent external attackers, says John Worrall, chief marketing officer for CyberArk.

"The advanced threat from the outside really goes south for [companies] once the attackers compromise an insider's privileged credential," he says. "So you really want to have real-time monitoring of behaviors -- then you can build these profiles of what is expected."

Similar to financial firms tracking credit-card usage, monitoring behavior allows companies to determine whether an employee's account exhibits irregular behavior. Logging in from a different country, outside of work hours or to several accounts in one session, are all likely signs of compromise, Worrall says.

[Top executives, power users, and IT administrators may have access to more than they should. Here are some tips for keeping them in check. See How To Monitor And Control Privileged Users.]

In addition, companies should look at their password policies and work to limit privileged access, Lieberman says. A single user should not be logged into his privileged account while doing day-to-day work. Rather, he should have to elevate privilege only when necessary. Taking that approach limits the exposure of that particular user and the account credential, he says.

"This is a matter of behavior, not a matter of technology," he says. "We have to spend a lot of time on training the behavior of our customers to operate their business in a sane way that gives them some resiliency."

Companies also need to survey their use of privileged accounts, searching for default passwords, backdoor accounts, accounts for workers no longer employed by the company, and accounts that are rarely, or never, used.

Companies also can work with their authentication providers to use the most appropriate type of security for privileged accounts. Mobile authentication provider Nok Nok Labs can query a mobile device and attempt to use the strongest possible type of authentication, a technique that helps secure the cloud service from attackers, says Brendon Wilson, director of product management for Nok Nok Labs.

"There is a bunch of advanced capabilities on mobile devices -- increasingly secure chips and secure elements -- all of these things can be used to make the authentication piece stronger, whether for an enterprise, a consumer business, or a Web service," he says.

Yet companies cannot just rely on strong authentication to keep out attackers. They have to assume the attackers are already inside their perimeters, Lieberman says.

"If you wake up every day knowing that someone is in your systems, and you shouldn't stop looking for them, then I think you have a pretty good chance of preventing a breach," he says.

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