(Sharecast News) - The UK's largest law firm has started proceedings against its insurer after it failed to pay out over a global cyberattack.The Petya ransomware attack in 2017 wiped out all emails and telephones at DLA Piper for two days, leaving lawyers unable to access systems. DLA is one of the world's biggest law firms, with 36,000 lawyers in 40 countries and clients ranging from multinational companies to government departments.However, according to The Times, its insurer Hiscox has refused to pay the firm's insurance claim, which is understood to be for several million pounds, and the two sides are now entering arbitration to resolve the matter.Cybercrime is a relatively new area for both companies and the firms that insure them, but is already a significant threat. According to Lloyds of London, the insurance market, cybercrime was estimated to cost businesses $450bn globally in 2016, with the global market for cyber insurance worth up to $3bn. Insurers wrote $1.4bn of premiums in 2016, noted The Times, a 35% hike on the previous year.However, many insurance policies contain clauses that means insurers do not have to pay out for an act of war, such as terrorism, and it remains unclear if cyberattacks can be classed as such.Both DLA Piper and Hiscox declined to comment.