The impact of Code Red and related viruses such as Nimda has caused over 150,000 IIS-based websites on around 80,000 different machines to disappear from the internet. It has also resulted in the closure of one of the most visible proponents of Microsoft technology for mass hosting.

According to the most recent Netcraft web server report, released this week, a significant number of sites running IIS fell off the web during the Code Red crisis.

The number of IIS servers hooked up to the internet went down even more when Webjump, an IIS-based virtual hosting service, went under. At the time it died, Webjump hosted around 280,000 sites.

Microsoft suffered a further blow on the back of this when analyst Gartner Group issued a strongly worded advisory recommending IIS users to evaluate alternative products.

Only around 2000 of the 80,000 IP addresses running IIS that disappeared turned up running a competing web server, indicating that users have yet to react to Gartner's advice.

Despite evidence to suggest that administrators have been securing their servers throughout a period of heightened worm activity, Netcraft's research "shows that numbers of vulnerable Microsoft IIS sites are actually starting to rise again, after the initial shock and disruption of Code Red prompted many sites to patch for the first time", said the company.

Of those high profile sites seen to switch from Microsoft platforms to Linux, the most noticeable are search engine Infoseek, and the FBI, which is pushing the secure Linux bandwagon anyway.

But the report did show that Microsoft still owns almost 50 per cent of the web server market, while Linux is in second place with almost 30 per cent. Next is Solaris and BSD with seven per cent and six per cent respectively.

"The trend is of Linux steadily increasing, Windows maintaining a large share, and the others slowly losing share," said Netcraft.

But while Microsoft may have the lion's share on a per machine basis, on a per site basis Apache is king. Because a great majority of the world's websites are located at hosting and co-location companies, and technically sophisticated hosting companies can run several thousand websites on a single computer, the result is more sites running Apache.

On this level, Apache holds 60 per cent of the market, while Microsoft only manages to hang on to 30 per cent.

Netcraft's September 2001 survey was based on data gathered from 32,398,046 websites and can be seen here.