By Mark Ward
BBC News Online technology correspondent
Home PC users will be able to get one of Microsoft's biggest software overhauls ever later this week.
The key update tightens security in Windows XP
The software giant has told BBC News Online that its SP2 security patch will be put on servers that automatically update home PCs as from Wednesday.
The consumer version is smaller than the business edition released to corporate customers in early August.
The software updates Windows XP and fixes many security loopholes exploited by viruses and malicious hackers.
Available to business
The SP2 update was first promised in 2003 but was only released to manufacturers earlier this month.
One of the big changes introduces in SP2 is a Security Center that lets people manage anti-virus software, firewall and key updates in one place.
Business users were the first to get their hands on SP2 and many had downloaded and installed the update once it was available.
CHANGES DUE IN SP2
Pop-up ads blocked
Revamped firewall on by default
Outlook Express, Internet Explorer and Windows Messenger warn about attachments
Origins of downloaded files logged
Web graphics in e-mail no longer loaded by default
Some spyware blocked
Users regularly reminded about Windows Updates
Security Centre brings together information about anti-virus, updates and firewall
Protection against buffer over-runs
Windows Messenger Service turned off by default
Early this week Microsoft let business users put the update on corporate servers that spool out updates to the machines sitting on internal networks.
Servers that let home users download the software are due to be switched on this Wednesday.
For consumers, SP2 is expected to be about 80mb but it could vary in size depending on how up to date with patches a user's machine is.
Microsoft hopes to get SP2 on to 100 million machines in the next couple of months.
By the end of the month users of XP Professional will get a version tailored for them.
Early reports suggest that SP2 can cause problems with some programs that expect to have net access.
The firewall in XP is turned on by default which could make these programs work differently, or stop altogether, once SP2 is in place.
Microsoft is advising users to turn on the automatic Windows update
Users having problems are advised to check Microsoft's S2 support pages to find out how to get software working again.
Common programs that SP2 has an impact on include many games, business applications and even some anti-virus software.
Microsoft recommends that people tidy up their PC before they install SP2 and make sure it is clean of viruses and spyware.
Although SP2 will help prevent against some future infections, it may not notice if a machine is already infected with malicious programs.