The website NBC.com was hacked Thursday and security experts warn that visitors to the site may have infected their computers with malicious software.
"We identified the problem and are working to resolve it," an NBC spokeswoman told The Huffington Post.
The spokeswoman did not know how long the website had been potentially spreading malware, but by 4 p.m., she said the site was "cleaned up" and no user information was compromised.
"Users who go on there now are safe," she said.
Security researchers caution that visitors to the site may have been hit by what is called a "drive-by-download attack," in which malicious software is downloaded onto their computers simply by visiting the website.
"Our research team is analyzing the case (and the malware) and we will post more updates soon," the security firm Securi wrote in a Thursday afternoon blog post. "What we can tell is that you should not visit NBC’s site right now," the firm wrote before NBC disclosed the hack.
The online security firm SurfRight said in a blog post that the malware, known as the Citadel Trojan, is used by cyber criminals for "banking fraud and cyber-espionage."
This story will be updated with more details when they become available.