Most users just don't bother trying to memorize all of those separate usernames and passwords for multiple Websites: Instead, 73 percent use the same password for their online banking account as they do on at least one nonfinancial Website, and nearly 50 percent use the same user ID and password, according to a new report.

Trusteer, which runs a browser security service, revealed the findings today based on a sample of more than 4 million users of its service during a 12-month period.

"Maybe it's the security guy in me, but I was surprised by the amount of sharing of usernames and passwords that take place," says Amit Klein, CTO of Trusteer and head of its research group. "This lends itself to attacks."

Around 65 percent of users reuse their user ID on nonfinancial Websites when their bank lets them create their own ID, and 42 percent do so on at least one other Website when the bank issues them the user ID.

"This has implications: Once these [shared] credentials are compromised in some way, other user accounts are exposed -- often they are sharing these same credentials with less secure and maintained sites," Klein says. All it takes is the user's credentials being harvested off of one of those sites, and the banking account is in jeopardy, according to Klein.

So how do users balance the nightmare of juggling multiple sets of credentials? Trusteer recommends consumers have at least three sets of credentials: one for financial Websites only, another for nonfinancial Websites that house sensitive information about the user, and a third for Websites that don't contain any confidential information about the user.

Financial institutions should identify and alert customers who reuse their online credentials on nonfinancial Websites and educate them of the risks, as well as set their risk engine to "higher sensitivity" to these users, according to Trusteer's report, which is available here (PDF).

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