All the information you provide with your ProJobs membership can only be seen by recruiters. Recruiters are members who use the XING recruiting tool. Recruiters from your current company are automatically blocked and cannot see this additional information or your job preferences. In the settings at https://www.xing.com/jobseeker-criteria/visibility, you can choose to block additional companies if desired.
All blocked users will not be informed that you are looking for a job, nor will they be able to see your job preferences and the additional ProJobs information on your XING profile. They also cannot tell that you are using the ProJobs membership.