Mozy has announced the days of its unlimited backup service are limited.  What the online backup provider used to sell “for the price of a hamburger” ($4.95 a month) is about to match Angus Beef prices.

Why the price increase?  Because people actually used the service to backup their hard drives.

“There has been a change in consumer behavior,” Russ Stockdale, Mozy’s vice president of product management, told CNET News. “What we have seen since we launched an unlimited service five years ago is there has been an explosion in digital content, specifically digital photos and video.”

The new plans, to be unveiled today:

• Mozy Basic: $5.99/mo for up to 50GB of data.  Each additional 20GB increment will cost $2 more per month;
• Mozy Multi-Machine: $9.99/mo for up to 125GB of data from up to three computers.  Each additional 20GB increment is also $2 more per month.

Earlier days.

CNET columnist Stephen Shankland is taking personal responsibility for the company’s price increase, noting he is among the service’s top 0.3 percent of users, backing up nearly 600GB of his digital media files — exactly the kind of customer Mozy wants to charge more.  His multi-year discount means the $3.40 a month he used to pay will now rise to $60.

Mozy’s competition:

• Google Docs costs $1,400 a year for 400GB;
• Google’s Picasa Web Albums costs $100 per year for 400GB.
• Jungle Disk, which provides a front end to storage using Amazon’s S3 service, charges a flat rate of $3 per month plus 15 cents per gigabyte per month.
• Carbonite, perhaps Mozy’s best-known competitor, throttles down bandwidth for big-data users.
• Dropbox charges $20 per month for 100GB.