"A small number of these customers had their PCs crash before their re-started backups were complete. These customers were not able to restore all of their files from Carbonite," the company said.

Carbonite said it took responsibility for the problem, apologized to the affected customers, and addressed the technical issues that caused it. In the statement, which seems to refer to one particular incident, the company said the event happened nearly two years ago and it hasn't encountered further problems since then.

Carbonite alleges breach of contract, breach of warranty, fraud, and deceptive acts and promises, and is seeking damages to be determined at trial. Interactive Digital Systems, a systems integrator in Norwell, Massachusetts, is also named in the suit. An attorney for Interactive Digital said the company had not yet seen the suit.