Shares in Arcontech Group plummeted over 30% on Thursday, after the financial market data service provider warned its full-year result are likely to be hit by a major customer's decision to terminate its contract almost two years early.The company said it remained uncertain over the level of profitability it can achieve in the second six months of the year, after a "significant customer" had requested to have its contract terminated 18 months early.The group declined to name the customer and the reasons behind the decision to terminate the contract, saying they were outside of their control."Although we expect to achieve new sales wins before the year end, due to revenue on our contracts being taken to profit on a monthly basis, it is unlikely that we will be able to fully compensate for the loss of revenue should the contract be terminated," Arcontech said in a statement.The London-listed group added that in the six months to 31 December it swung from a pre-tax loss of £66,735 to a pre-tax profit of £116,932.Revenue edged higher 2.4% to £1m, while administrative costs declined 7.4% to £925,699.Arcontech shares were down 32.26% to 0.105p at 09:20 on Thursday.