McAfee has apologised to users for bugs in the company's line of client-protection software, released in the US last month. The product will be released in the UK this month, and has already been patched prior to European customers getting their hands on it.

In an email sent to some US users last week, McAfee executive vice-president Bill Kerrigan acknowledged that there had been glitches in the rollout. "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 fixed software, which is going through a phased rollout, according to a McAfee spokeswoman. 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 antivirus market, hoping to stay one step ahead of their new competitor. With this new line of products, code-named 'Falcon', McAfee introduced an updated 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 software didn't work well with some ISP software, causing browsing slowdowns for some users, the company said. And customers who had disabled firewall protection would be presented with notification messages that could not be ignored – an annoyance for some.

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."

McAfee's UK PR agency told PC Advisor: "When this pioneering new range was launched in the US earlier this summer, a number of initial glitches were experienced by a limited number of customers. No computer protection systems were compromised and McAfee worked quickly to address the problem, deploying automatic fixes to the issues caused by the upgrade.

"A phased rollout process ensured that any potential issues to arise could be dealt with prior to full release. As a result, no customers purchasing any of the new European consumer product range have experienced these problems as the patch has been released prior to launch."

US 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. "One out of every 10 images would not load unless I refreshed the page a number of times," he said. "I was frustrated to the point where I no longer had any interest in trying to fix a program that should have helped my computer stay alive."

Even before this latest update, Saefkow had experienced problems running FTP (file transfer protocol) and P2P (peer-to-peer) software on his PC, but the web-browsing bug was the last straw, he said. He has chronicled his difficulties with the software on his blog.

He now plans to remove the McAfee software and download a free product, which he hopes will be less of a drain on his PC.

"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."