Hundreds of millions of computers around the world are now vulnerable to security breaches and other forms of sabotage after Microsoft abandoned support for the Windows 7 operating system (OS) that powered them.
Microsoft first released Windows 7 in 2009, mainly to address the massive failings in the bug-ridden Windows Vista OS that preceded it.
It ended up considerably better received by users and critics (but again compared to Vista this is not difficult), fuelling Microsoft's track record of releasing operating systems that are good (Windows XP, 7, 10) after ones that are bad (Vista 8).
On Tuesday the company ended extended support for Windows 7, meaning if you're one of almost 400 million people estimated to still be using the operating system you'll no longer receive security updates, leaving your PC vulnerable to hackers and scammers as well as malware and viruses.
When Windows 10 was released in 2015, Microsoft gave out free updates to users on Windows 7, 8 and 8.1, giving them a year to get on to the latest operating system for free.
While this program officially ended in 2016, many user reports online suggest you can still take advantage of the offer via the Microsoft website, which is particularly advisable if you're on Windows 7.
Otherwise, a fresh copy of Windows 10 will set you back A$225 ($234.38) for the Home tier and A$339 for the Pro version.
The pricier version comes with more features, including remote encryption if you lose your device.
Microsoft has previously stated it wants to have Windows 10 running on more than one billion devices, a goal it is expected to hit this year after eclipsing 900 million last September.
Despite being installed on the majority of the world's PCs, Windows is only the second most used operating system behind Google's Android OS that powers more than 2.5 billion smartphones and tablets around the world.
The update to Windows 10 is recommended to maintain the security of your computer but not everyone updates.
Some users remain on even older versions of Windows.
Late last year, for instance, photos emerged purporting to show Russian President Vladimir Putin still using the Windows XP operating system first released in 2001.