A UK cryptocurrency startup that raised $40m (£30m) has been hit by a cyber attack that has shut investors out of their accounts for several days.

Electroneum, which offers a digital currency that can be mined using smartphones, was due to launch its website and mobile app last Thursday, having crowdfunded millions of dollars in bitcoin and ether following a so-called "initial coin offering", or ICO.

The Maidstone-based company's website came under a distributed denial of service (DDoS) cyber attack last week, forcing it to delay the full launch of its mobile mining app.

DDoS attacks involve a network of compromised computers, known as a "botnet", which flood a website's servers leaving legitimate traffic unable to get through and making the website vulnerable to hacking.

Electroneum, which claims 140,000 people hold its tokens, has locked down the accounts while it tries to bring its network online safely.