Chiara said:

L/GPL'ed license. you have to contribute back to if you fix something or modify code.

Sorry Chiara but it's false :-) From the GPL FAQ:

The GPL does not require you to release your modified version. You are free to make modifications and use them privately, without ever releasing them. This applies to organizations (including companies), too; an organization can make a modified version and use it internally without ever releasing it outside the organization.

But if you release the modified version to the public in some way, the GPL requires you to make the modified source code available to the program's users, under the GPL.

Thus, the GPL gives permission to release the modified program in certain ways, and not in other ways; but the decision of whether to release it is up to you.

The GPL requires that if someone gets legally a binary of a GPL product, he/she can get the source code of the application for a fee covering the expenses of reproduction, from the people/organization who made the build. With the source code, he/she can do what he/she wants in the limit of the GPL (you can't put further restrictions) and the copyright laws.

The viral aspect is a different part. That's why I think they should do a LGPL FAQ.