On the day the stock market gained $1.1 trillion, Robinhood went down for 17 hours

Stocks rallied Monday with the Dow logging its biggest point gain in history. But an all-day system-wide outage left Robinhood customers seething.

An "issue with a part of our infrastructure" caused the 17-hour long disruption, the company said in a statement. The service has about 10 million customers.

"We realize we let our customers down, and we're committed to improving their experience," a Robinhood spokesperson said. The app and website has resumed normal operation, according to a tweet posted Tuesday.

Robinhood told customers in an email that their funds in their accounts are safe and personal information was not breached. Despite those reassurances, people slammed the app on Twitter. Some called the outage "ridiculous" and other demanded compensation.

In response, Robinhood is compensating some affected customers with billing credits. It's also giving premium members three months worth of service for free. The premium tier costs $5 a month.

The outage is another black eye for Robinhood, which caters to young people and is valued at nearly $9 billion. FINRA, Wall Street's self-regulator, recently fined Robinhood $1.25 million for sending customer trading orders to four broker-dealers without guaranteeing the best price.

Robinhood's existence has helped revolutionize the stodgy trading industry. It has forced established players to abolish commissions and even sparked the blockbuster merger of Charles Schwab and TD Ameritrade.