McAfee has apologised to users for bugs in the company's new line of client protection software, released last month.

In an email sent to some last week, vice president Bill Kerrigan acknowledged that there had been glitches in the roll out. "We would like to extend our sincere apologies to anyone who may have had problems with their computers due to the upgrade," he wrote.

Not all McAfee customers have been given the new software, which is going through a phased roll out, according to a McAfee spokeswoman, and none are in Europe. However, users who receive software updates from McAfee directly, or who purchased the software in the past month may have had problems, she said.

Both McAfee and rival Symantec have been contending with Microsoft's recent entry into the anti-virus market, hoping to stay one step ahead of their new competitor. With this new line of products, codenamed Falcon, McAfee introduced a new user interface as well as its SiteAdvisor website rating software.

McAfee estimates that fewer than one percent of customers who downloaded the new software have had difficulties, but the problems they experienced could be annoying.

The new software didn't work well with some ISP software, causing browser slow-downs. And customers who had disabled firewall protection would be presented with annoying notification messages that could not be ignored. Some customers were simply confused by the new user interface, McAfee added.

"While we believe no one’s computer protection was compromised, we have worked quickly and hard to resolve the issues," Kerrigan said. "In fact, we have already sent out an update that automatically fixed the glitches caused by the upgrade."

Customers who have complained about the bugs are being offered a free three-month extension to their subscription, a McAfee spokeswoman said.

The bugs made Web surfing a drag, said Matt Saefkow a programmer in Cleveland. "When McAfee itself is causing a computer to feel like it's affected [by malicious software] that's counterproductive," Saefkow said. "I'm not going to be spending money on antivirus."