After a year or more of preparation, home users can now get their hands on the SP2 security update for Windows XP. Here BBC News Online answers some of the most common questions about the package.
If you auto-update you should be able to get hold of SP2
What is SP2?
The full name is Service Pack 2 and it is a software package that makes lots of changes to Microsoft's Windows XP operating system. Since Windows XP was launched in October 2001, the software has proved to be something of a virus writer and hacker's playground. SP2 is a bid by Microsoft to remove many of the bugs that make XP so vulnerable to attack. The Service Pack was first promised in 2003 but has taken a year of testing to get ready.
SP2 is one of the most visible parts of Microsoft's Trustworthy Computing initiative. This aims to make Windows harder for hackers and virus writers to exploit. Ironically since Microsoft announced this initiative its software has suffered some of the biggest virus outbreaks and hack attacks ever seen.
What does SP2 do?
The update makes lots of changes to Windows XP. Some are visible, others not. One of the most obvious changes is the creation of a "Security Center" that lets people manage firewall, anti-virus and updates for XP in one place.
It also lets users know the risks they are taking if they do not have the firewall turned on, do not update their anti-virus software or install future updates for XP.
Anyone that connects an unprotected PC to the net via a high-speed link is taking a huge risk. Studies have shown that unprotected PCs are typically found and attacked within 20 minutes of being put online.
The update also blocks pop-up ads and makes it much harder for spyware to download on to your computer. Users will also get warnings about potentially malicious attachments on e-mail messages or programs that attempt to install themselves without permission
Out of sight SP2 also makes changes to the way Windows XP handles data to make it much less vulnerable to viruses that, for instance, exploit its willingness to run programs attached to e-mail messages.
Where can I get SP2?
Only from Microsoft. The software, which for consumers weighs in at about 80MB, can be downloaded via its auto-update service, ordered on a CD or found on cover CDs that come with some consumer technology magazines.
Efforts to help Microsoft reach people with SP2 by putting the update on file-sharing networks were squashed by the software giant.
Business users were the first to get hold of the update and the consumer version is being released this week. Users of the Professional version will have to wait until late August to get a version tailored for them.
How will it affect my computer?
It should protect you from some, not all, attacks on Windows by virus writers and malicious hackers. However, if you install it on a PC without making sure the computer is free of spyware, viruses and the like then you might be no more secure.
Also many of the most successful viruses play only on the gullibility of e-mail users rather than exploit bugs. The SP2 update will stop some, but probably not all, of the malicious attachments on e-mail messages that help viruses spread.
A German magazine has found that the update still leaves inventive hackers a route to infect Windows and it is probably only a matter of time before these loopholes are exploited.
Installing the patch might make some of the programs you have got used to using on your PC stop working properly. Microsoft has produced a list of programs that suffer, to a greater or lesser extent, when SP2 is installed. Surprisingly many of the programs affected are Microsoft programs.
Microsoft does give advice about how to get these programs working again but the advice could prove too tricky for many users.
So should I install SP2?
Probably. Windows is a hugely tempting target for virus writers, malicious hackers, clever criminals and many others. With SP2 you can probably avoid falling victim to many of the most obvious viruses, attacks and scams.
However, you should not think that once you have installed SP2 that you are immune from future attack. If you have not cleaned up your machine before installing it and your machine has been compromised you may be no more secure than before.
As well as installing SP2 you need to keep your anti-virus software up to date and ensure you have other critical updates to Windows. Use anti-spyware programs to regularly clean up your PC. You should also be suspicious about e-mails from friends or acquaintances that you were not expecting and that have attachments.
You should also find out if you use any of the programs that SP2 conflicts with and see if you have the skill to carry out the steps necessary to get that program working again.