Just when it looked like hack attacks on Microsoft systems might be falling, new figures have been published showing the number of successfully compromised Windows boxes is actually on the rise at an alarming rate.

Although the number of successful attacks on Windows machines fell broadly through the first quarter of this year, June saw an increase of five per cent in compromised systems compared to the previous month, while successful hacks in July rose by a further 12 per cent.

According to recent figures compiled by the Intelligence Unit at analyst mi2g, Linux was the hottest target for hackers throughout April and May. But throughout June and July the trend has reversed and Windows is once again the most vulnerable operating system when it comes to internet attacks.

Attacks on Linux systems actually dropped by 39 per cent in June.

The analysts said that the temporary rise in successful attacks on Linux boxes was because of a rash of exploitable vulnerabilities discovered in open source third-party applications such as PHP and Apache. Although the Apache vulnerabilities affected Windows systems too, it appears that swift action on the part of the vendors of affected products and administrators of Linux machines ensured a significant decrease in the number of successful attacks.

"The recent Apache vulnerabilities have affected both Windows and Linux systems. Online administration is about overall configuration management. At one level it is about patching the known vulnerabilities of the OS and the server software that runs on top. At another level it is about selecting reliable third-party applications so as to stop them from being used as a launch pad for deeper penetration," said DK Matai, chief executive of mi2g.

Out of almost 30,000 successful attacks recorded by mi2g this year so far, 47 per cent were on systems running Windows, 36 per cent were on Linux systems and 17 per cent were on miscellaneous others such as Unix, BSD and Solaris.