Google phases out support for IE6
Microsoft say support for IE6 will continue for the next four years
Google has begun to phase out support for Internet Explorer 6, the browser identified as the weak link in a cyber attack on the search engine.
The firm said from 1 March some of its services, such as Google Docs, would not work "properly" with the browser.
It recommended individuals and firms upgrade "as soon as possible".
Google threatened to withdraw from the Chinese market following the "sophisticated and targeted" attacks, which it said originated in China.
Hackers used a flaw in Microsoft's Internet Explorer (IE) browser to target the Gmail accounts of Chinese human rights activists.
Following Google's revelations, the French and German governments advised their citizens to switch to a different browser until the hole had been closed.
Microsoft reacted by quickly updating the browser, nearly three weeks ahead of its regular security update.
However, Google has now said it is going to phase out support for the browser "starting with Google Docs and Google Sites".
It said that as a result, some "key functionality" of the applications would not work when used with IE6.
Google Docs is the firm's answer to products such as Microsoft Office, whilst Google Sites allows people to create web pages.
"The web has evolved in the last ten years, from simple text pages to rich, interactive applications including video and voice," wrote Google's Rajen Sheth in a blog post.
"Unfortunately, very old browsers cannot run many of these new features effectively."
Around 20% of web users still use the nine-year old browser, including many UK government departments.
But many developers want to see the browser phased out as soon as possible.
The online campaign ie6nomore, supported by more than 70 web firms, says that because the browser does not support modern web standards it restricts what developers can do and is "holding the web back".
Microsoft has said that it will support the browser until 2014.
Microsoft has released a fix for Internet Explorer and recommended that customers install the update as soon as possible or update to the latest version of the web browser for "improved security".
Microsoft normally issues patches monthly but the high-profile nature of the attacks led it to act more quickly.
The UK government downplayed the threat and said there was "no evidence that moving from the latest fully patched versions of Internet Explorer to other browsers will make users more secure".
However, Microsoft took the unusual step of patching the hole nearly three weeks ahead of its regular security update.
The new patch is available via the Microsoft Update site and will also be fed out to those who have their machines set to update automatically. All versions of Internet Explorer will receive the update.
Microsoft has admitted that it has known about the vulnerability "since early September" 2009 and had planned to patch it in February.
The bad publicity has allowed rivals such as Firefox to gain market share.
According to web analytics company StatCounter, Firefox is now a close second to Internet Explorer (IE) in Europe, with 40% of the market compared to Microsoft's 45% share.
In some markets, including Germany and Austria, Firefox has overtaken IE, the firm said.
Mozilla, the foundation behind Firefox, has just released the latest version (3.6) of the open-source browser.
This is interesting, is google hoping to force the issue so other major sites drop support for it.