Zotero was created with the philosophy that your research data belongs to you and should be kept secure and private by default.
All Zotero software is open-source and can be audited for security and privacy practices.
Unlike many cloud-based tools, the Zotero desktop application is a local program that runs on your computer and saves all research data locally by default. Unless you explicitly set up syncing, your research data never leaves your computer.
If institutional policies prevent uploading of data to third-party servers, Zotero can always be used locally without syncing any data, but syncing is required to use group functionality.
If you choose to sync your data with the Zotero servers, all data is encrypted in transit with current best practices (Zotero receives an A+ score on the well-respected SSL Labs test) and stored within the Amazon cloud, where access is tightly restricted to the few people who need access to maintain the service. All data is currently stored in the us-east-1 AWS region in Virginia.
While library data can be synced only with Zotero servers, for syncing of attached files you can choose between Zotero servers and a WebDAV server under your control, or you can use linked files that are stored in a location of your choosing and aren't synced by Zotero.
The Zotero data server is open-source and can be run locally, which some organizations choose to do, but this can be technically challenging, and we don't currently provide support for such installations. We hope to provide additional support for local server installations in the future.