Dropbox

Arguably the most convenient thing about Dropbox is how universally integrated it is with everything. Most websites or software have utilized some kind of Dropbox integration to sync your files or create backups. In regards to those complaining about privacy/security, although relevant concerns, it should be noted that this is a non-issue if you encrypt your data before uploading. This seems to make more sense to me than trusting a third party that "says" they keep your data private. Unless they've verified that, I don't see why anyone should assume trust, let alone deny themselves of superior features. If you encrypt your files yourself before uploading to Dropbox (or any other backup/cloud software really), there's no reason to worry about trusting a third party when you yourself have verified the legitimacy of your data security.

Dropbox syncs your files between multiple computers. It became popular early on in this market and has maintained brand awareness and loyalty, despite newcomers (esp. Google Drive). It's fast and convenient but it comes at a terrible privacy & security cost. See below for details and alternatives.

Privacy and Security Concerns

Dropbox, Google Drive, etc. use a model of storing your data that isn't private. Files are uploaded to their servers and then encrypted using keys that Dropbox/Google Drive keep. At any point they can access your files. This is inherently insecure and privacy-hostile. It means hackers who access the data and the key can read your files. And it means Dropbox/Google (and similar services, e.g. SugarSync) have to comply with National Security Letters, which force them to give up your data to intelligence agencies without even telling you.

Some of the other problems Dropbox has had in providing a secure or private service:

• In 2011 there was an FTC complaint that Dropbox's privacy policy misled customers because their practices allowed successful intruders to view others' files.
• In 2011 there was a bug so serious that customers' data became accessible without even requiring a password.
• In 2013 Dropbox was hacked, compromising an employee account, and from there users' data.
• In 2013 it was revealed that the NSA planned to add Dropbox to its PRISM surveillance program, which forces companies to give up data on their users (see comments above) For all we know, that's now happened.
• In 2016 it was shown that in 2012, 68.7 million user accounts were hacked.

There's plenty more. Dropbox have a terrible record of protecting people's security and privacy and being honest it.

More Private Alternatives & Value for Money

Tthere are plenty of alternatives that offer a far more secure model, with end-to-end encryption (ie, the service cannot access your data, also known as a "zero-knowledge" policy because your files are encrypted before being uploaded not after and the company doesn't have the keys). Most of these services offer more than Dropbox's 2GB for free:

• Sync.com: Easily the most "Dropbox-like" service that offers end-to-end encryption. Canadian-based. Offer 5GB for free. Disadvantage: no Linux client. Good mobile app, though.
• iDrive: Good for backup and syncing computers using selected folders. End-to-end encryption. US-based (but can't give files to NSA or lose them to hackers if they don't have the keys to your data). 5GB free, 1 year 1TB package for only $50. No Linux client though. Excellent mobile app. Backs up your photos, contacts. Brilliant.
• SpiderOak: End-to-end encryption/"zero-knowledge" model that keeps your data safe. US-based. 250GB for free for 21 days as a trial. After that, $5/month for 100GB; $12 buys 1000TB (similar to Dropbox). Spideroak is best suited for backups. Works on Mac, Windows and Linux. You can setup folders to sync between your computers. SpiderOak's mobile app is limited, allows you only to download files, not upload.
• Tresorit: Tresorit are most expensive. Based in Switzerland (strong privacy laws). Sync multiple folders with end-to-end encryption. You can send people "encrypted links" which reveal files you want to share only to the intended recipient. They also held a hacking contest. No one was able to hack them after 468 days for a $50 k bounty. It used to be possible to get the business package for 2 users, then reduce the number to 1 before the first free month ran out.
• pCloud: Very much like Dropbox but Switzerland based. Cheap. (10 GB for free, up to 20GB with bonuses for referrals). For $50 you get 500GB/year. For $4/month or so, you get the Crypto folder, which is end-to-end encrypted (they can't access it). This is more limited than the options above (it's only one folder), but that might suit you and the overall price is very good. pCloud has a mobile app comparable to Dropbox in functionality. pCloud's client is available for Mac, Windows and some Linux distros (although you can get it for other distros though their respective repositories, or just unpack the .deb file from the pCloud website).
• Seafile.de (go to Seafile.de not Seafile.com, which is where the AlternativeTo page points to): This is a great Dropbox alternative. Hosted in Germany (better privacy laws than US). Their client software works on Mac, Windows and Linux and is open source & it has a mobile app every bit as functional as Dropbox's. It even has the option to encrypt folders before they get uploaded (However, only file contents, not names, sizes or structures, are encrypted - see Cryptomator below). Prices are low: 10 GB costs €1.05, and 500 GB costs €5.25.

How to Protect Your Files For Services That Don't Offer End-to-End Encryption

Whichever service you go with (Dropbox, GoogleDrive or any of the above), you can protect your privacy by uploading only encrypted version of your files by using one of these apps:

• Cryptomator: Cross-platform (Mac, Linux, Windows) app that creates an encrypted "vault" out of a folder you specify. In the encrypted vault, you place your files and only after opening it with a password can you view your files in a mounted virtual drive.. It's free, open source. A mobile app is in beta.
• Duplicati: More for backups than sync. Select a folder for Duplicati to monitor. It makes backups to a destination folder (inc on a USB drive, Dropbox, whatever you want). You can have it encrypt the backup files, which is great if you plan to sync to the cloud (for reasons discussed above). Works on Wn, Mac & Linux.

Syncing Stuff Occassionally Between Computers To sync files between 2 computers, just occasionally use SyncThing has you covered. Free, open source, runs on Win, Mac & Linux (opens in the web-browser). You tell it which folder to sync and then pair it with the other computer by typing in a code. The two computers will find each other online and sync the folder(s). The connection is direct (data doesn't sit on anyone else's server) and encrypted. Speeds of up to 80MB/second!