(Reuters) - FXCM Inc, an online foreign exchange broker, said its systems were hacked and a "small number" of unauthorized wire transfers were made from customer accounts, sending the company's shares down 25 percent to a record low.
All funds have been returned to the accounts that were compromised, the company said on Thursday.
FXCM said it received an email from a hacker claiming to have illegal access to customer information and that it had notified the Federal Bureau of Investigation.
An FBI spokeswoman said the bureau was "aware of the incident and is investigating."
FXCM said it was working with a cybersecurity firm to determine the scale of the incident and identify affected customers.
The company did not say when it was hacked or give any further details on the incident. FXCM did not immediately respond to a request for comment.
FXCM is the latest U.S. corporation to become a victim of a cybersecurity attack, adding to a list that includes Target Corp, Apple Inc and JPMorgan Chase & Co.
Accusations against China have increased amid growing concerns about national security. Last week, U.S. President Barack Obama and his Chinese counterpart Xi Jinping signed a pact to fight cyber warfare.
FXCM's shares were down 4.6 percent, recouping some losses after hitting a record low of $6.51. The stock had fallen about 95 percent this year mainly due to losses stemming from the Swiss National Bank's removal of the cap on the Swiss franc in January.
(Reporting By Sudarshan Varadhan in Bengaluru; Editing by Saumyadeb Chakrabarty and Savio D'Souza)