A security researcher claims that all Fortune 500 companies have been hacked

Mikko Hypponen, the chief research officer at F-Secure Oyj, claimed in an interview with Bloomberg that all Fortune 500 companies have experienced successful hacks.

"How many of the Fortune 500 are hacked right now? The answer: 500," Hypponen said. "They all have security breaches, big or small. If you have a big enough infrastructure, you won't be able to secure all of it."

The TalkTalk hack, which has knocked off almost 7% of the company's value, is the latest in a long line of security breaches that include US retailer Target, T-Mobile, Apple, Walmart, Neiman Marcus, and more.

While TalkTalk may have been an easy target, other companies - such as banks - have been urged to increase security. In 2014, J.P Morgan was hacked because the company hadn't implemented two-factor authentication, a process which uses both the users phone and a PC to log-in.

Other UK firms, such as EE, told Bloomberg that the hack had left it unaffected due to "robust security measures."