Generate an appropriate single-sentence summary for the given text such that it includes the main topic of the text.

From the high of $260 (£169) for each bitcoin on 10 April, bitcoins are now worth less than $100 (£65) each. The main bitcoin exchange shut down for 12 hours to install hardware to help it cope with trading volumes. In addition, malicious software is emerging that seeks out and empties the virtual wallets of bitcoin owners. MTGox, on which most bitcoin trading takes place, was overwhelmed earlier this week by the amount of people who joined the exchange to trade the virtual cash. The computer problems prompted a round of panic selling that forced values to plunge. The exchange went offline to beef up its hardware to cope with trading volumes and stem the fall in value. However, soon after trading resumed the site came under a sustained hack attack which saw it bombarded with data. In a tweet, MTGox said the it was being hit by a "stronger than usual" attack. It went offline again to avoid the attack and when it re-started, bitcoins continued to fall in value. Early on 12 April each bitcoin was worth about $90 (£58). 'Litecoins' Owners of bitcoins have also become the target of cyber thieves keen to cash in on the boom in the digital currency. A phishing gang posted a message to the discussion forum of a website used by many bitcoin traders saying MTGox was about to start trading "litecoins" - an alternative to bitcoins. In the message was a link that supposedly connected to an official MTGox chat site. In fact, the site that people were taken to if they clicked on the link was fake and, via a booby-trapped update file, installed malicious software that then emptied digital wallets of bitcoins. At least one trader was hit in the attack and lost 34 bitcoins as a result. In a post about the theft posted to the Bitcointalk forum, the victim said he was "stupid" not to have taken more trouble to stay safe but added: "This is a serious loss for me, and unless this is handled correctly this can also badly affect the community." It has also emerged that Tyler and Cameron Winklevoss, who famously sued Facebook founder Mark Zuckerberg claiming they had the original idea for the social network, have substantial bitcoin holdings. In an interview with the New York Times, the pair said they owned about $11m of the virtual coins - about 1% of the global supply.
The bitcoin virtual currency has had a volatile 24 hours that saw values plummet, hack attacks, trading shutdowns and bitcoin-stealing malware.

The total cost is expected to be £60m, with the Westminster government paying the rest of the bill. The announcement came after talks between Mr Wilson and Treasury Minister Danny Alexander in Belfast. World leaders will gather at the Lough Erne resort outside Enniskillen on 17 and 18 June for the economic summit. "We have put in place funding arrangements which makes sure the government is picking up the large majority of costs," Mr Alexander said. "This is a national event and we are grateful to people here for hosting it." Some Policing Board members have expressed concern that there would be an impact on normal policing if the PSNI carried any costs associated with the huge G8 operation. Mr Alexander also said that he did not anticipate the PSNI's budget being reduced by an upcoming national spending review. Several years ago, the Treasury provided additional finances for counter-terrorism. "I understand the need and we will make sure whatever is required is provided," he said.
Finance Minister Sammy Wilson has said hosting the G8 summit this month will cost the Northern Ireland Executive around £6m.

The CAA's chief executive Andrew Haines said he was "furious" that the airline had not been complying with the law - by failing to offer to re-route passengers on rival airlines. Ryanair cancelled up to 50 flights a day through to the end of October, affecting 315,000 passengers It then cancelled another 18,000 flights between November and March, affecting the travel plans of another 400,000 passengers. All of Ryanair's flights are short or medium-haul, and the vast majority are to destinations within the EU, meaning that passengers are entitled to some very specific rules on compensation. What are my options if my flight is cancelled? You can apply for a refund. Even if it is only the outbound portion of the flight that is cancelled, you can still get a refund for the return leg, assuming you do not want to use it. Or you can chose an alternative flight - perhaps on an earlier or later date. In most cases Ryanair will offer you another flight with them. However, the Civil Aviation Authority (CAA) says that if Ryanair fails to offer a place on an alternative Ryanair flight within a reasonable timeframe then you have the right to be booked onto a different airline at no extra cost. Should I get a refund and arrange my own alternative flight? You are free to do this, but you will then lose out on any right to compensation, and probably be out of pocket as the alternative flight is likely to be more expensive by now. Consumer group Which? says that it is best to make Ryanair do the legwork - rather than cancel the Ryanair flight, rebook yourself on another airline, and try to reclaim any extra cost from Ryanair if the new flight is more expensive. By doing so, you might only get a refund for the cancelled Ryanair flight. I don't know whether my flight has been cancelled: What should I do? Ryanair says it has sent emails to all those affected. There is a dedicated page on the Ryanair website where there are also links to forms to fill in for alternative arrangements. If you decide to cancel or change your flight without knowing whether it will be cancelled officially, you have no special rights under the European Regulations. For that reason, the CAA advises passengers to go through the airline. Can I claim extra compensation for the inconvenience? You can claim compensation - but it is based strictly on the time of your actual arrival compared to when you originally expected to arrive. It also depends on when Ryanair told you about the cancellation. In the first wave of cancellations, many passengers were given less than a week's warning, so would have been entitled to compensation under EU rules, even if they were then found a flight with another airline. If the airline gave you more than 14 days' notice, it does not have to pay any compensation at all. As more than two weeks' notice has been given for the November to March cancellations, affected passengers will not be entitled to the extra compensation. What if I have received less than 14 days' notice? If your re-booked flight arrives more than four hours later than the flight you were originally booked on, you can claim 250 euros - around £220. For flights over 1,500km, known as medium-haul, that goes up to 400 euros - around £350. However, if the new flight re-routes you via another destination, and you end up with a longer flight as a result - you can still claim compensation, but at a lower rate. If you are flying on a short-haul flight, and the re-routed flight is at least two hours late, you can claim 125 euros - around £110. If a medium-haul re-routed flight is at least three hours late, you can claim 200 euros - around £176 - depending on the time of take-off. What if I have received less than seven days' notice? If you receive less than a week's notice of the cancellation, the criteria for compensation are tighter. In this case, your short-haul flight only needs to arrive more than two hours after your original scheduled arrival time for you to claim 250 euros. If flying more than 1,500km, and the flight is at least three hours late, you can claim 400 euros. If a new short-haul flight is re-routed, taking off more than one hour before your original flight, but arriving two hours after it, you can claim 125 euros. A re-routed medium-haul flight needs to arrive at least three hours late for compensation to be paid. In such a case passengers would get 200 euros. Am I entitled to additional help? If you find yourself stranded at the airport, you might also be entitled to an extra payment to cover short-term costs. For example, if you have had to wait an extra day to take the new flight you should be given accommodation, food, drink and access to communications - such as the cost of a couple of telephone calls.

Ryanair has said it will co-operate with the Civil Aviation Authority (CAA) to ensure passengers are aware of their rights when flights are cancelled.

