Since I am not a lawyer, the following statements are my personal opinion and my own experiences. It is not a legal advice. If specific questions or problems arise, you should contact a lawyer.
Private Salary Data exchange with colleagues is no longer a taboo.
Many workers prefer to keep it for themselves - but who wants, can freely talk to colleagues about his salary.
The boss can not force anybody to secrecy, now ruled by a court in germany.
Quote: "You cannot forbid employees – either verbally or in written policy – from discussing salaries or other job conditions among themselves.
Discussing salaries is considered a “protected concerted activity” by the NLRB and it’s protected regardless of whether employees are talking to each other in person or through social media."
You have the right to address work-related issues and share information about pay, benefits, and working conditions with coworkers on LinkedIn, Xing, Facebook, Google+, YouTube, and/or other social media platforms like "SDE".
Keep this in mind.