This modules creates a plUpload dialogue on a given page. One or more files, also really big ones, can be uploaded; big files are chunked into smaller parts during upload to avoid trouble with server-sided restrictions. Furthermore, you can configure where the uploaded files should be stored, if uploaded pictures should be downsized on the fly and whether only registered users should be able to upload files or any visitor of the site.
The filenames are randomized with a huge amount of characters during upload, so it's nearly impossible to overwrite existing files or guess the name of uploaded files, and of course you can (and should!) restrict the allowed file types to harmless extensions like image oder plain text files.