SiSustainable

Why should a CMS be Open Source ?

First of all, Open Source CMS’s are free, which can significantly decrease cost.

Furthermore, for a long term project, at some point some problems may only be solved by modifying the source code of the CMS. In Closed Source software the source code is usually made to be as incomprehensible to humans as possible, in order to make it difficult to copy. In Open Source the source code is usually written to be as accessible as possible with further documentation to help so any problem, no matter how difficult, will have a solution.

So if you want, it’s really easy to convert the database of one Open Source CMS to another Open Source CMS. Often, a small program to do so has already been written and is available for free. So, if ever it was simpler to change CMS’s rather than modify the source code, this is a possibility. Obviously the goal is to never modify the source code and never change CMS’s, since these two tasks will be the most expensive and risky.

Security

Since the source code is open (and explained), anyone can look at it and find practical or theoretical weaknesses. Since computer code can be incredibly complicated it may take thousands of people to make it secure. In most cases weaknesses are resolved while still only theoretical and before any example of it being exploited even exits.
In Closed Source software it’s impossible to afford to pay thousands of people to review the code, nor afford to show or explain the code to by-passers or their users (lest someone copy it). With Open Source many by-passers look at the code simply out of curiosity, and often a significant portion of the users look at the source code out of interest or in order to change it in some way.
There is no system 100% secure but there are very few viruses in Open Source and very few ways to get them !