For a full-featured file upload service with security, you should also consider Filestack. It offers a range of features like virus, copyright, phishing, object and explicit content detection, as well as OCR for data extraction. The service can accept uploads from local disk, cloud storage and device cameras, and offers a customizable interface and SDKs for programming languages.
Another good option is Uploadcare. This full-featured file management service offers secure delivery and access control, malware and NSFW filtering, and user authentication. It also offers AI-powered image operations and automated document conversion, so it can be used as a good foundation for scalable and flexible projects.
If you need a service with strong security and collaboration abilities, Dropbox is a good option. It offers protected file storage with version history, password protection and watermarking. Dropbox also offers real-time document analytics, secure collaboration and a range of plans for different needs, including personal and business use.