Microsoft has released a service update for all versions of its Windows Vista operating system.
The update may cause problems for some PCs running Vista
The computer giant claims that the update improves the stability, security and performance of the software.
The update, or service pack, includes some fixes released before now and adds many new ones as well.
Microsoft has warned that the update could clash with some security software and other programs customers may have installed on their machine.
Those using Vista can download the update directly from Microsoft or wait for it to be automatically installed on their machine in mid-April.
On the Windows Vista blog, Nick White, Microsoft's product manager for the software, said those installing Service Pack One (SP1) may have to download and install some other "prerequisites" before the update can be applied.
The pre-requisites are generally updates to other programs or components of Vista to ease the passage of SP1.
Mr White also warned that some device drivers may also have to be refreshed before SP1 can be installed. Old drivers from RealTek AC, Intel and Symantec are known to stop SP1 being installed.
PROGRAMS HIT BY SP1
Fujitsu Shock Sensor
Jiangmin KV Antivirus 10
Jiangmin KV Antivirus 2008
Zone Alarm Security Suite
Iron Speed Designer
Rising Personal Firewall
Novell ZCM Agent
Advice about drivers and prequisites is provided on the Vista blog and in support articles.
In late February Microsoft released a list of programs that SP1 could break when it was installed. Among those listed were anti-virus programs from BitDefender and Trend Micro.
A spokesman for Trend Micro said the issue had now been resolved.
Some other programs, such as Iron Speed Designer, will stop working when SP1 is installed. Others, such as the The New York Times Reader, will also lose some functions.
Vista SP1 is being released initially in only five languages - English, French, Spanish, German, and Japanese. Another 31 will follow in mid-April when the software starts being pumped out to those that have their PCs automatically updated.
Microsoft recommends that Vista users go to Windows Update to get the service pack rather than use its download service.
The version available via Windows Update is only 65 MB in size (compared to 434MB via download) and can diagnose driver problems before installation.