San Francisco: People clinging to Microsoft’s aging Windows XP operating system will be left to fend off cyber criminals by themselves starting tomorrow.

On April 8, the US software colossus will stop patching newly found security holes in Windows XP code that hackers could exploit to slip into computers.

Despite Microsoft’s long-heralded plan to stop “supporting” the nearly 13-year-old operating system, it still powers from 20- to 30 per cent of Windows machines around the world, according to industry estimates.

“I am sure you have everything from police departments to banks to legal offices to restaurants,” Trustwave director Christopher Pogue said while discussing the extent to which Windows XP is still used.

“Think of a business and they probably run XP; I would say everyone is in equal danger.”

US-based Trustwave specialises in helping businesses fight cyber crime.

Microsoft support entails regular security updates, but when it stops issuing patches to defend against freshly revealed hacker tactics aimed at XP, those using the operating system will need to enlist their own software wizards or live with mounting threats.

Hackers might already know of new ways to break into XP-powered computers but be waiting until after Tuesday to attack because Microsoft will no longer step in to thwart them, security experts say.

“You are talking literally millions of computers systems that will cease to receive regular security updates,” Pogue said.

“That is obviously causing a panic because of new vulnerabilities that will be introduced.”

Microsoft has released several generations of Windows since XP made its debut in 2001.

The most recent version is Windows 8, tailored for a world enamored of touch-screen computers and services hosted in the Internet “cloud.”

Given the rapid evolution of computer hardware and the short lifespans of devices, newer computers bought by consumers are likely running newer versions of Windows.

Of concern, though, are small businesses that stuck with XP because they have grown accustomed to it and it gets the job done.