A faulty update to Symantec's Norton security software began booting thousands of users off their AOL internet connections last week, Symantec has admitted.

The problem began with a March 15 intrusion detection signature file sent via LiveUpdate to customers using Norton AntiVirus and Norton Internet Security, according to Symantec. The file caused Norton to mistakenly identify AOL traffic as malicious, effectively blocking Internet access for both dialup and broadband customers.

"A Symantec Intrusion Detection signature that was included in the March 15 LiveUpdate caused this problem," said Symantec in an advisory on its website.

Symantec said it released an updated signature file fixing the problem about seven hours after the first file was distributed. However, without a connection, those affected weren't necessarily able to access the fix.

AOL's U.K. call centers have received around 4,000 calls about the problem, according to a spokesperson.

The solution is relatively simple, according to Symantec -- users need to update their Norton software, which should enable them to go online and download the corrected signature file. Detailed instructions are available in the company's advisory, which, sadly, will not be accessible to those affected.

Symantec is in good company with regard to update gaffes. The previous week, McAfee's virus-scanning products wreaked havoc on corporate and consumer systems, after a buggy virus definition file triggered the quarantine or deletion of a long list of executable files, including Microsoft Excel.

While excel.exe was the most high-profile false positive, the list of wrongly identified files later released by McAfee was seven pages long. Administrators said they expected to spend hours restoring the quarantined files.