Following further flaws in Microsoft’s security, Windows users are being urged to update and download the latest security patches to protect themselves.
In Microsoft's monthly security update five patches are strongly advised for installation, four labelled as "critical".
Some commentators believe that this months flaws are so serious they can be used to hijack a Windows PC without the user's knowledge.
The five updates issued in April are for users of Windows Vista, XP, 2000, Server 2003 and Microsoft Content Management Server. These patches have been released early to prevent anticipated criminal hacking.
Microsoft says that not downloading these patches could lead to "remote code execution" which means hackers can exploit them to take over a PC, steal information or put it to their own uses.
Windows is regularly found with security problems, this update includes a new version of a patch released in early April that had been causing problems for some users.
Security updates from Microsoft appear every second Tuesday of every month.