Hackers successfully breached an unnamed financial service and stole data for six months before being detected, according to security firm Darktrace.
Dave Palmer, director of technology at Darktrace, who has worked for MI5 and GCHQ, told V3 that the breach is a sign that many firms still fail to adequately protect their systems.
"There was a financial institution we were working with, where in the first week we found a problem with data leaking," he said.
"We took a quick look at it and tracked it to a piece of malware that wasn't particularly stealthy. From its install [date] it had been there for six months. This is a common scenario."
Palmer explained that Darktrace sees attacks like this on an almost daily basis, and said it is a sign hackers are becoming increasingly bold in their movements.
"We're seeing increasing [incidents] where data servers are getting compromised and pushing data out to the internet on a daily basis," he said.
"People are so confident in firewalls that companies aren't looking inside their networks. A lot of times with these attacks it's not sneaky, it's bold faced data extraction."
Disturbingly, Palmer said that many of the attacks are opportunistic, rather than targeted, and only succeed because of human error or poor security.
"We're seeing a surge in certain types of attacks being successful, in particular malvertising, ads catching people out on legitimate sites," he said.
"Unless you're running the latest operating systems even surfing the web can catch you out. We're reporting this to customers every day.
"This is people seeing who they can get rather than specifically targeting them, but once they get somebody in an organisation, they will move and see if they can monetise the information you've got.
"Or if they're an ideologically motivated group seeing if they can deface your site or break your systems."
Palmer highlighted the recent attack on Sony Pictures Entertainment as proof of his claim.
The attack occurred in December 2014 when #GOP hackers leaked vast amounts of Sony data, including partners' personal information and the terms of its deal with Netflix.
Reports suggest that the hackers managed to access so many of the firm's systems as Sony stored passwords in an unprotected file labelled 'passwords'.
Palmer said that businesses should learn from Sony's mistakes and begin adopting more robust security practices.
He added that firms with sensitive data should also employ intelligence-based security systems that can detect unusual behaviour.
"[The idea is to create an] immune system that lets you know something is going on in your system and give you the tools to let you know if it's legitimate, risky or malware," he said.
"[For example, our system uses] self-learning mathematics and machine learning with systems absorbing activity from every machine and person and creating individual baselines about what is normal behaviour."
Darktrace is one of many firms to highlight the need for intelligence-based systems. BAE Systems paid a huge £144.4m for cloud security provider SilverSky in 2014 in a bid to improve its threat detection and analytics tools.
Meanwhile, SAP highlighted possible uses of its HANA cloud platform for spotting atypical employee and system behaviour.
Palmer said that, while the cloud does offer benefits, companies dealing with sensitive data are justifiably wary of the move.
"We're extremely firm believers that, if you have sensitive data, you want to have control and know where it is," he said.
"People that are most actively targeted, be they government or financial services, are not interested in data going somewhere else.
"[For example] we have healthcare customers, one of which works with patients' genetic sequencing data, and we can't see them loading that into a cloud."
Palmer is one of many IT professionals to warn against the dangers of the cloud. Bank of England CIO John Finch urged businesses in 2014 to consider the regulatory, security and monetary concerns with cloud computing before adopting it.
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