Robinhood users have faced a series of attacks on their trading accounts in recent weeks.
Bloomberg News reports that an internal review estimated the number of compromised users near 2,000.
According to Business Insider, the online trading company has not disclosed an exact number.
Robinhood security says security "is a top priority and something we take very seriously."
In response to the breach, Robinhood has started encouraging users to implement two-factor authentication.
The number of compromised accounts is a small fraction of the company's 13 million users.