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Computerworld - If your New Year's resolution was to make sure you have secure offsite backups for your important data at home, then relax: There are a number of good, reliable (and inexpensive) services on the Web that offer ways to keep your information safe.

"Using an online backup service is a convenient way to preserve your key files," says Greg Shulz, senior analyst at StorageIO, an IT analyst firm. "It is an increasingly popular way to make sure you never lose a file."

Online backup services offer several advantages over backing up to an external hard drive. The data itself is actually safer than at your home or office because it's stored in a secure facility. If your home or office is damaged or destroyed -- by a fire, say -- the data is out of harm's way. Plus, most data centers have backups of your backups in case there's a disaster at the data center.

To ensure security, online services usually encrypt incoming data using 128-bit SSL encryption; once stored in a secure server farm, all the services then secure files with 256-, 440- or 448-bit encryption. Carbonite and Mozy use 448-bit Blowfish encryption, although Mozy also gives the option of 256-bit AES encryption where only you know the key. IDrive uses 256-bit AES, while SOS gives the choice of 256-bit AES or 440-bit AES encryption.

Because the data flows over the Internet, it can be slow going. "Don't be in a hurry," warns Shulz. "Plan on having a lot of time handy; backing up and restoring files online can be painfully slow."

While an initial backup can take a day or more, the subsequent additions take much less time because only the new or changed files need to be transferred to the backup service. And, as with local backups, most of the work happens in the background.

Online backups do have their limits, though. For example, if you want to copy the contents of your hard drive or do a complete backup, you may want to look beyond the less feature-filled services. In fact, three of the four online backup services reviewed here -- Carbonite, IDrive and Mozy -- concentrate on preserving personal files and ignore program coding and the all-important operating system. SOS can back up an entire PC locally to an external drive (but it can't backup program coding or OS data to the online service).

How I tested

To see how these four online services compare, I used a Toshiba Satellite L755 notebook with Windows Vista Home Premium.

I first backed up the notebook using a Western Digital 320GB hard drive connected externally to the system and Norton Ghost 14 (so that I could restore the notebook to its original state after each test).

I set up a wired Internet connection via a cable data service, a 100Mbps Linksys router and a Level One switch. Typical download and upload speeds of the network were 10Mbytes and 2Mbytes, respectively.

I timed how long it took to perform an initial backup of the system with 22GB of data. Next, I added 24.5MB of data to the system, simulating the changes that someone might make in a day or two, and timed how long it took to make the incremental backup. In order to check how it affected system resources, during a backup I watched a video, wrote some documents and ran the Speedtest.net bandwidth meter (which is fairly resource-intensive).

I then deleted a file and timed how long it took the online backup system to find it and then to restore it. Finally, I restored the system over the service, timing how long it took.