ION Group, the financial data firm's parent company, said in a statement on its website that the attack began on Tuesday. "The incident is contained to a specific environment, all the affected servers are disconnected, and remediation of services is ongoing," ION Group said, declining requests for further comment. ABN told clients on Wednesday that due to "technical disruption" from ION, some applications were unavailable and were expected to remain so for a "number of days". It added that its staff had to process trades directly with the exchange. Intesa Sanpaolo told clients that its brokerage and clearing operations on exchange-traded derivatives had been "severely hampered" by IT problems at ION and that it was not able to handle orders.

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