Welcome to the ODK forum, @Tarektrabelsi! We're glad you're here. When you get a chance, please Introduce yourself here! I'd also encourage you to add a picture as your avatar because it helps build community 
Central never shares collected survey data. Also, by default, Central does not send any usage information to the ODK team. You can choose to share anonymized usage analytics with the team, and helps them make Central better for you! See Usage Reporting in Central for more details.
You may also be interested in reviewing the documentation page on ODK Security.