Staff at US chain Target reportedly failed to stop the theft of 40 million credit card records despite an escalating series of alarms from the company's computer security systems.

Bloomberg Businessweek claims that security technology from FireEye detected the malware-powered hack – but Target staff failed to act on the alerts, only taking action after a warning from federal investigators around two weeks after the initial breach at the end of November.

FireEye's technology could have auto-nuked the Target malware but the functionality was disabled. The FireEye system was installed six months prior to the breach and it could be that Target's security team hadn't yet got to the point where they trusted it to act semi-autonomously.

Failure to act on alerts from security systems, such as FireEye's technology or intrusion detection systems, is a common operational failure. The issue is complicated by the prevalence of false alerts from security technologies. The specifics of the Target breach, as explained by Businessweek, cast security practices at the massive US supermarket chain in a particularly unflattering light.

"On November 30th, according to a person who has consulted on Target's investigation but is not authorized to speak on the record, the hackers deployed their custom-made code, triggering a FireEye alert that indicated unfamiliar malware: malware.binary," Businessweek writes. "Details soon followed, including addresses for the servers where the hackers wanted their stolen data to be sent. As the hackers inserted more versions of the same malware... the security system sent out more alerts, each the most urgent on FireEye's graded scale."

Target's Symantec anti-virus system also flagged up alerts about suspicious activity around the time of the initial breach, which ultimately exposed 70 million pieces of personal information as well as 40 million credit card records.

The supermarket employed a team of security specialists in Bangalore tasked with monitoring its computers around the clock. Any problems were supposed to be reported to Target’s security operations centre in Minneapolis, Minnesota.

A Target spokeswoman conceded lack of action over the initial alerts was a mistake. "With the benefit of hindsight, we are investigating whether if different judgments had been made the outcome may have been different," the spokeswoman told Reuters.

In a blog post, FireEye (whose technology spots malware by running files through a parallel computer network on virtual machines) declined to say whether or not Target was one of its customers or to comment directly on the Businessweek story.

Bloomberg Businessweek reported on the methods hackers used to steal millions of credit card numbers from Target. In the report, FireEye was mentioned as having discovered the attack prior to the broad discovery by Target as well as providing services to the CIA. It is FireEye policy to not publicly identify our customers and, as such, we cannot validate or comment on the report’s claims that Target, the CIA or any other companies are customers of FireEye.

The Target breach has been narrowed down to a specific malware tool (a modified version of BlackPOS) that affected its point-of-sale systems and, according to some security experts, enterprise payment processing servers. Multiple versions of the tool were used. If Target's security staff acted earlier, even on the second alert, they would likely have been able to prevent hackers siphoning off millions of credit card records to servers hosted in Russia.

Investigators are working on the theory that the initial breach of Target's systems was carried out after first hacking into the network of its supermarket refrigerating system supplier, Maryland firm Fazio Mechanical Services.

At least one security staffer raised worries about the state of Target's payment terminals around two months before the breach but these concerns were "brushed off", The Verge adds. It's unclear what these concerns were, or whether or not they were relevant to the mega breach that hit weeks later.

Target is pushing towards installing improved credit card security systems in the aftermath of the breach. The supermarket has also joined the Financial Services Information Sharing & Analysis Center, an industry group designed to pool knowledge and best practice to help the detection, prevention and response to cyber attacks and fraud activity, among other initiatives.

Target's chief information officer, Beth Jacob, stepped down in early March. Around the same time the firm began efforts to recruit a Chief Information Security Officer. ®