A hacker extracted customer log-in credentials from a server owned by Bitdefender that hosted the cloud-based management dashboards for its small and medium-size business clients.
The antivirus firm confirmed the security breach, but said in an emailed statement that the attack affected less than 1 percent of its SMB customers, whose passwords have since been reset. Consumer and enterprise customers were not affected, the company said.
The hacker, who uses the online alias DetoxRansome, first bragged about the breach on Twitter Saturday and later messaged Bitdefender threatening to release the company's "customer base" unless he was paid US$15,000.
To prove his point, the next day he published the email addresses and passwords for two Bitdefender customer accounts and one for an account operated by the company itself.
Travis Doering and Dan McPeake claimed in a blog post that they contacted the hacker, who offered to sell the data to them.
The hacker provided a list of user names and matching passwords for over 250 Bitdefender accounts, some of which were confirmed to be active, the two wrote Wednesday.
Doering and McPeake said that they shared the information with Bitdefender
According to them, when they asked DetoxRansome how he obtained the log-in credentials, he replied that he was "sniffing" one of Bitdefender's "major servers."
Bitdefender confirmed that the attack did not exploit a zero-day vulnerability -- a vulnerability that is previously unknown.
The issue was the result of human error: During an infrastructure increase, a single server was deployed with an outdated software package that had a known flaw, enabling the extraction of information, but not a full system compromise, said Catalin Cosoi, chief security strategist at Bitdefender.
He declined to name the vulnerable package.
The issue was resolved and additional security measures have been put in place to prevent its reoccurrence, the company said in its statement. "Our investigation revealed no other server or services were impacted."