Chinese hackers hit Forbes.com

For three days late last year, the news site's "Thought of the Day" widget, which appears when readers visit the site, was compromised -- seamlessly redirecting visitors from certain organizations to another site where their computers could be infected with malware without their knowledge.

Forbes acknowledged the incident. "On December 1, 2014, Forbes discovered that on November 28, 2014, a file had been modified on a system related to the Forbes web site," the outlet said in a statement. "The file was immediately reverted and an investigation by Forbes into the incident began. Forbes took immediate actions to remediate the incident." The news outlet's investigation found "no indication of additional or ongoing compromise nor any evidence of data exfiltration," according to the statement.

The hack comes amid growing concerns that even the most trusted sites can be used by hackers aimed at infiltrating sensitive industries.

Using Forbes.com was "fairly brazen" and a shrewd move, said Steve Ward, senior director at iSIGHT Partners. "It's a trusted place that all of the employees in a targeted organization are going to be allowed to go to," he explained.

The attack worked by leveraging two undisclosed coding flaws -- typically called "zero day" vulnerabilities.

The first was a problem with Adobe Flash, which the company patched December 9th, and the second was an Internet Explorer flaw, which Microsoft released a fix for on Tuesday. The Internet Explorer flaw was deployed by the attackers when the Flash flaw alone was not enough to compromise targeted visitors' systems.

The hack redirected some of the site's visitors to a malicious site where their computers were silently attacked by malware. The researchers said they believe the malware was only used to infect a select group of targets, despite the broad audience of Forbes.com, which is ranked among the top 200 most visited sites globally by Alexa. The researchers said they confirmed the attack targeted at least some companies within the defense and financial services industries although it's possible its reach was larger.