"A problem was identified and it has been fixed," an NBC Universal spokeswoman told Reuters. She declined to elaborate on the nature of the problem.
Earlier on Thursday, several security experts had advised Internet users to avoid the site altogether, saying it had been compromised by malicious software.
The Dutch computer security firm SurfRight said on its HitmanPro blog that the site of its NBC television network was tainted with viruses known as the Citadel and ZeroAccess that are used for banking fraud, cyber espionage and other computer crimes.
The NBC spokeswoman said she could not confirm whether any users had been infected. But she said that no account information about users of the site had been compromised.
Earlier in the day, Facebook Inc blocked users from accessing the NBC.com website following reports that the site was infected with a computer virus.
Facebook users were told "This link has been reported as abusive" on Thursday when they attempted to access the NBC.com website.
NBC is controlled by Comcast Inc, which is buying out minority owner General Electric Co.
(Reporting By Jim Finkle and Jennifer Saba; Editing by Gary Hill, Bernard Orr)