Researchers at McAfee have been working with some of the victim companies to investigate the attacks. They discovered the new IE vulnerability during the course of the investigation. The flaw was used in a sophisticated attack that included victims receiving targeted emails with malicious attachments or links to malicious sites, which then exploited the flaw in IE. Google was the first to publicly disclose the attack on Tuesday, saying that its corporate network had been compromised. Adobe also disclosed an attack Tuesday, but has not confirmed that it was related to the same series of attacks that hit Google and more than 30 other companies.
Source: https://threatpost.com/google-attackers-used-internet-explorer-zero-day-011410/73374/