Dropbox had 'detected' that employees at our company were using Dropbox and it would be unfortunate if their stored files were no longer available and it would be in our best interest to sign up for a business account or we might legally be in breach of some terms of service. Some detective work later it was determined that people had been signed in to Dropbox from company machines, but there were no accounts opened with a company email and nothing business related was being synced. All Dropbox binaries and network connections have been blocked since.