In a direct quote from Carbonite's website:
"As part of our ongoing security monitoring, we recently became aware of unauthorized attempts to access a number of Carbonite accounts. This activity appears to be the result of a third party attacker using compromised email addresses and passwords obtained from other companies that were previously attacked. The attackers then tried to use the stolen information to access Carbonite accounts.
Based on our security reviews, there is no evidence to suggest that Carbonite has been hacked or compromised."
For more detailed information and instructions on what you should do, please visit the original blog post on their website by clicking here.