An attack this week that targeted online customers of at least 50 financial institutions in the U.S., Europe, and Asia-Pacific has been shut down, a security expert said Thursday.

The attack was notable for the extra effort put into it by the hackers, who constructed a separate look-alike Web site for each financial institution they targeted, said Henry Gonzalez, senior security researcher for Websense Inc.

To be infected, a user had to be lured to a Web site that hosted malicious code exploiting a critical vulnerability revealed last year in Microsoft's software, Websense said.

The vulnerability, for which Microsoft had issued a patch, is particularly dangerous since it requires a user merely to visit a Web site rigged with the malicious code.

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