The amount of money spent on support for the open source operating system Linux will reach $1.3 billion by 2013, according to a new report from technology market researcher IDC, representing a compound annual growth rate of 16.9%.

That good news for commercial Linux vendors such as Red Hat and Novell was tempered by the finding that the number of Linux deployments for which the user does not pay support fees is growing faster than paid deployments.

And according to the report, that growing number of nonpaid deployments includes versions of the Linux operating system that are only available commercially, which implies that some organisations are using the software illegally.

Another study published this week by the Linux Foundation found that Red Hat, Novell and IBM are the top three contributors to the operating system’s source code. Linux originator Linus Torvalds is no longer in the top 30 contributors.