Carbonite Inc., a Boston company that backs up computer data for businesses and other organizations, is alleging that two other companies sold it more than $3 million worth of defective hardware, resulting in thousands of customers losing data.

In a lawsuit filed in Suffolk Superior Court this week, Carbonite said it suffered "substantial damage" to its business and reputation from products manufactured by Promise Technology Inc. and marketed to Carbonite by Interactive Digital Systems Inc.

Carbonite's complaint charged Promise Technology with breach of contract, fraud, and unfair and deceptive acts and practices. The complaint charged Interactive Digital Systems with breach of warranty. It seeks unspecified damages against the two companies.

Promise's hardware was meant to monitor multiple computer hard drives to assure that they were functioning properly to preserve customers' data, according to the suit. Instead, the suit charged, "Carbonite lost the backups of over 7,500 customers in a number of separate incidents, causing serious damage to Carbonite's business and to its reputation as a reliable source for backup data service."

The suit said Promise engineers were unable to fix the errors. "The problems that have occurred have required Carbonite's senior engineers, senior management, and senior operations personnel to spend enormous amounts of time dealing with the problems," it said.

An executive at Promise denied the Carbonite allegations yesterday.

"We stand by our product," said Chi Chen Wu, senior vice president of Promise. "We looked into the claims and found there was no merit to the allegations." Wu said the company was continuing to investigate the matter.

Representatives of Interactive Digital Systems in Norwell didn't return phone calls. The companies have 30 days to respond to Carbonite's complaint.

Carbonite's attorney, Thomas I. Elkind, yesterday said the defective hardware included a limited warranty that guaranteed it would perform to specifications for three years after the purchases.

"This was supposed to recognize defects, take down the hard drive, and transfer data to another hard drive before it was lost," said Elkind, a partner in the Boston office of the Foley & Lardner law firm.

"It certainly didn't perform to the specifications that were represented."

Robert Weisman can be reached at weisman@globe.com.

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