Computer hackers attacked the Hong Kong Stock Exchange's regulatory disclosure website yesterday, crashing the site and forcing the suspension of trading in shares of seven firms with a combined market value of HK$1.5 trillion - including HSBC Holdings. 'Our current assessment is that this is the result of a malicious attack by outside hacking, but we have no information as to where the hacking attacks came from or the motives behind them,' Hong Kong Exchanges and Clearing (HKEx) chief executive Charles Li Xiaojia said yesterday. Last night, HKEx said it had contacted police about the matter. With market volatility running at its highest levels since the global financial crisis, three blue-chip firms - HSBC, HKEx (the stock exchange itself) and Cathay Pacific Airways were affected. Together they account for 18 per cent of the Hang Seng Index. Trading was also halted in 419 warrants or other securities - worth an estimated HK$200 million - that are tied to the underlying shares of the affected companies. The stocks were suspended because the seven firms attempted to make announcements of price-sensitive information during the lunchtime trading break, which investors may not have seen due to the hacking incident. The exchange's trading platform was not targeted. 'We understand some investors would not be happy with the trading suspensions ... but that was the best way to protect all investors,' Li said. Cathay and HKEx were announcing their financial results for the first six months, while HSBC announced a US$32.7 billion deal to sell its US credit card business. The four other companies whose shares were frozen were China Power International Development, China Resources Microelectronics, Dah Sing Banking and Dah Sing Financial. The apparent attack on the Hong Kong exchange's website follows a successful hacking of Zimbabwe's stock exchange site less than a week ago, and hacking attacks on the websites of the London and Nasdaq stock exchanges early this year. 'When we have more details the interesting thing to see will be whether time-sensitive information was taken, presumably on what company results were to be released before the attack,' said Michael Gazeley, co-founder and managing director of Network Box, a Hong Kong-based managed security services provider. 'Recent [global] hacking attacks have just been about vandalism or releasing information for no particular reason. This may be about financial gain,' he said. The Hong Kong attack targeted HKEXnews.hk, the stock exchange's official and only site for all regulatory filings and disclosure announcements made by the city's 1,463 listed firms, as well as by 5,712 other types of securities including warrants, callable bear/bull contracts and bonds. Listed companies are also required to maintain individual websites where they must cross-post their stock exchange announcements. HKEXnews.hk began experiencing problems around noon yesterday and remained largely inaccessible throughout the day. The exchange moved quickly to establish a back-up website, bulletinboard.hk, where it is currently posting notifications when regulatory filings have been made. But web users must visit the site of the company in question in order to download and view the content of the filing. Also inaccessible were so-called 'disclosure of interest' filings, which show trading in shares by company directors or substantial shareholders. The freeze on trading in shares riled investors and brokers who were looking to cash in their positions in the afternoon, as the market rebounded 2.34 per cent yesterday from Tuesday's 5.66 per cent sell-down. From about 7pm the HKEXnews site looked to be back online, but the backup website was also still being used. Shares in all seven of the affected firms would resume trading this morning, said HKEX's head of listing, Mark Dickens.