There’s an advantage to having copies of your files out on the Web — in the “cloud,” as they say rather nebulously. They’re away from your home or office, so you’re safer from fire and other catastrophes. If you store them on a decent site, it will have its own backups. Online backup is cheap and sometimes free.

Like any good, cheap thing, online storage has its drawbacks. One concern is security. Someone could intercept your files in transit, or break into the storage site, and grab them. If you’ve got serious confidential information on them, such as credit cards, Social Security numbers, and passwords, this can be very bad. In some places, such as Massachusetts, it’s illegal to store what’s called “High Risk Confidential Information” or HRCI offsite without taking certain precautions. On the other hand, in some cases, such as medical services, you may be required to have offsite backup and to make sure it’s secure.

You can get some security by encrypting your files. Be sure that the encryption key is a good one and that it’s available to those who may need it, possibly years later, and not available to anyone else, including the backup site.

Online storage may go away unexpectedly. Omnidrive, a company based in Australia, was once highly regarded for its Web-based storage service, but it went away in 2008 without warning, along with all the files stored on it. It hasn’t been the only one.

When you start using an online backup service, be sure to test its restoration features early on. After a disaster happens isn’t the time to discover you’ve been copying files into a black hole.

Don’t look at a site’s terms of service. These exist to protect the site owner and guarantee absolutely nothing. The terms of service from Iron Mountain, one of the most reputable storage companies, say:

Neither Iron Mountain, any of its affiliates, directors, officers and employees, nor any other party involved in creating, producing or delivering the Site is liable for any direct, incidental, consequential, indirect or punitive damages arising out of your access to, or use of, the Site or the operation of the Site or failure of the Site to operate. In no event shall Iron Mountain be liable for any direct, indirect, special, punitive, incidental, exemplary or consequential, damages or any damages whatsoever, even if Iron Mountain has been previously advised of the possibility of such damages, whether in an action in contract, negligence, or any other theory, arising out of or in connection with the use, inability to use or performance of the information, services, products and materials available from this Site. These limitations shall apply notwithstanding any failure of essential purpose of any limited remedy.

What you need to look at, if you’re paying for the service, is the Service Level Agreement (SLA). These will, for the better sites, promise you reimbursement if service fails to live up to a specified standard. Not all sites post theirs online, but you should make sure to see it before committing to any money. At best you’ll just get part or all of your money back, which can be scant consolation for losing your files, but it’s an incentive for the company to meet its obligations. If you’re using a free service, then of course there’s no guarantee of any kind.

Internet bandwidth is a factor to consider. If you have lots of frequently changing files to back up, you may need to get a faster connection to keep up.

As with a local drive, you’re best off automating your backup so you don’t have to remember to do it. Most services offer software that will let you do this. Make sure the software offers reasonable security and doesn’t send your password in cleartext. Make sure you understand what it’s backing up: Some services back up your whole drive by default, possibly including stuff you don’t want anyone else to have a copy of, even encrypted. Stuff you keep for … artistic reasons.

Don’t just save and forget. Check occasionally on news about your backup service, so you don’t get caught by surprise if it gets sloppy, is acquired, or goes out of business.

Suggestions: If you take suitable precautions and make Internet-accessible services a part of your backup strategy, your data can be safer than before. But don’t make the “cloud” your primary backup plan if you don’t want your files to go up in smoke. Use more down-to-earth techniques for long-term storage.

Personal note: On Sunday, February 19, I’ll be on a panel at the Boskone science fiction convention on “Digital Estate — Virtual Property OR On the Internet, Nobody Knows You’re Dead.”