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It is possible for users who are not in your organization to commit source code to your DevOps repository if the repository is set to allow external contributors. External contributors are users who are not members of your organization but have been granted access to your repository.
To check if your DevOps repository is set to allow external contributors, you can go to your repository settings and click on the "Options" -> "External contributions" section.
If the "Allow external contributors" checkbox is selected, then external contributors are allowed to contribute to your repository. If the checkbox is not selected, then only members of your organization can contribute to your repository.
To check who has access to your repository and what level of access they have, you can go to your repository settings and click on the "Manage access" tab. From there, you can see a list of all users and groups who have access to your repository and what level of access they have been granted.
If you want to remove a user's access to your repository, you can click on the user's name and then click on the "Remove" button. You can also change a user's level of access by clicking on the "Edit" button next to their name and selecting a new access level.
Hope this helps.