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Have you heard their ads? They sound like a scam just from that.

Not just their ads. There are all kinds of small claims on their web site that smell like snake oil. Stuff like: "We encrypt your files twice before backing them up securely offsite, using the same encryption techniques that banks use."

Twice? Really. I guess if once is good, then twice is better?

If you're in the market for something like this, I suggest taking a look at allmydata.com. It costs more ($10 per month for unlimited storage, rather than $5), but unlike Carbonite and Mozy it keeps all of your data forever, rather than deleting files 30 days after you delete them from your computer. It gives you a web-based "Time Machine" view that lets you see your data as it was on any given date.

Allmydata is also very geek-chic, since it's all open source, and uses erasure coding on your files to ensure reliability even if a server (or seven!) die. I believe they use a 3-of-10 scheme, where 10 shares of each file are distributed across 10 different servers, and any three of them are enough to recover the file.

Disclaimer: I don't work for allmydata.com, but I am using their distributed file system software to build my own P2P backup solution, to make it easy for groups of friends and family to set up their own backup systems by sharing parts of their drives over the net. The allmydata developers are very supportive of this effort, even though it's a potential competitor with their commercial offering.

*** Potential bias alert: I'm involved in both the Tahoe project at allmydata.org and the commercial online storage service at Allmydata.com ***

I wanted to add to the above comment that we (Allmydata.com) also tried out a business model where the software agent on each machine was a peer storage node on the storage grid. For many of the reasons that have already been mentioned, this model did not gain acceptance. Technically, peer node churn is logistically complex to efficiently manage, and socially it is difficult for people to accept storage of strangers' data (encrypted, encoded, or not). We now use the p2p storage grid only on servers that we manage and the clients are effectively encryption and transfer agents. This gives us a cost-advantage on the server side (easy to manage, cheap hardware can be used), but doesn't expose us to some of the other marketing and technical issues.

I would recommend taking a good look at Tahoe, from allmydata.org. This is an open source project that uses a conceptually similar file dispersal system for backup, but it has been designed and reviewed by expert cryptographers. There is also a commercial version available at allmydata.com which has generously sponsored the open source project. Tahoe is working on Windows, Mac, Linux and other Unix style systems.

Tahoe does have a minimal dependency on a central server to first learn about the peer nodes that hold data, but only for the initial callup - once the client is running, it remembers all the peers it is using. And they are working towards eliminating even this dependency with "gossip" introductions, so if you can connect to any peer you can learn of all the others. Everything is cryptographically protected with encryption and signatures to make it effectively impossible for anyone to see the contents of your files without your permission.

The current incarnation of these ideas can be seen in the Allmydata service, which uses Tornado/Raptor codes (very advanced forward error-correction) to split up the data. There are several problems with using Rabin's IDA for this purpose, ones which bit us in the ass several times and which I think might end up causing problems for this system...

Funny, I've been thinking of doing the same. P2P encrypted backups.

I give you... All My Data. Its distant cousin (Mnet) is still around, but sorta moribund.

Related companies/projects happened in this order: MojoNation .. MNet .. HiveCache .. AllMyData

good luck!

I've tried Allmydata in the past and had some success. They use a peer-to-peer system to back your files up. The free plan requires a 10:1 ratio (you share 10 megs, you get 1 meg). Not bad if you have a lot of free drive space sitting there doing nothing. I think it uses bittorrent as its transfer method but I can't remember exactly how it works and the web page is short on details.

I just got the most recent version (1.3) and haven't played with it much but the last one I had a lot of trouble with, sometimes files wouldn't upload, it was hard to tell if the program was actually working or if it had died, and it seemed like it couldn't remember which files I had chosen to persistently back up.

Still in beta though, but interesting if they can get the kinks worked out.

How does this sound?

You store my data, I will store yours.

Error-corrected and replicated so that 50% of the cloud could disappear and you would still have 4 or 5 nines of reliability.

Per-file, content-dependant encryption (e.g. every file gets its own AES encryption key)

Free accounts have a 10:1 provided vs. consumed ratio (to cover replication and error-correction bloat, with the ratio expected to drop over time) and people who want to buy a better ratio or even not have to provide space can do so.

Access to data backed-up by any of your systems from any other system you have installed the software on. (No more need to fiddle with system-to-system sync to make sure you have access to all of your files.)

Sound interesting? If so, head over to Allmydata and sign up for the beta test. [Windows only at the moment, but OS X and Linux versions will be available in a couple of months...]

A solution similar to the one suggested in this page is already being beta tested. Windows-only at the moment, but that will change. Based on the same technology that BitTorrent was derived from...