LastPass, a popular password management service, said hackers stole encrypted copies of customer passwords and other sensitive data such as billing addresses, phone numbers and IP addresses.

The announcement is the latest update from a breach that occurred in August. At that time, the company said they had seen no evidence that the hackers had access to customer data or encrypted password vaults.

But the company’s statement on Thursday said that source code and technical information that were stolen as part of that hack was used to target another employee. The hackers were then able to obtain credentials and keys to access and decrypt data stored on a third-party cloud storage space.

They were able to copy such things as basic customer account information, including e-mail addresses and the IP addresses from which customers accessed LastPass, and “fully encrypted sensitive fields such as website usernames and passwords, secure notes and form-filled data”.

Password managers are a way for customers to store usernames and passwords in one place and can be accessed using a master password that a customer creates. The master password isn’t known to LastPass nor is stored or maintained by the company, it said in its statement.

The other encrypted data can only be decrypted “with a unique encryption key derived from each user’s master password”, the company said.

Nonetheless, LastPass warned customers that they could be targeted for social engineering, phishing attempts or other methods.

Brute force

“The threat actor may attempt to use brute force to guess your master password and decrypt the copies of vault data they took,” the company said in a statement. “Because of the hashing and encryption methods we use to protect our customers, it would be extremely difficult to attempt to brute-force-guess master passwords for those customers who follow our password best practices.”

For those who follow LastPass’s password guidance, “it would take millions of years to guess your master password using generally available password-cracking technology”, the company said.

A representative for LastPass didn’t respond to messages seeking comment.

Read LastPass’s latest blog post on the incident

The company said that it has hired cybersecurity firm Mandiant to investigate the breach. It also said that it is rebuilding its entire development environment from scratch, an indication that hackers had thoroughly comprised the company’s sensitive systems.