The critical flaw only affected Microsoft's Windows 2000 operating system and it required users would have to visit a website and install a program that could then run malicious code on their computers.
The other security vulnerabilities, affecting MSN Messenger and Windows Live Messenger, were considered "important". The IM flaw allows hackers to run malicious code on computers if users click on an instant message link inviting them to check out a video.
When the punter accepts that invitation, the vulnerability kicks in. Instant messaging programs are proving a good target because people are starting to wise up to the fact that clicking on attachments sent in e-mails is likely to get you into trouble. µ