Third-party sellers on Amazon account for more than half of the site's sales. They've also become a target for hackers.
According to a Wall Street Journal report, online attackers have been changing bank deposit information on sellers' accounts and using stolen passwords to post fake deals.
We don't know how many fraudulent sales have happened, but some sellers reported losing as much as $50,000.
Security experts say there are simple steps that help protect against fraud and fake deals. If you're selling merchandise online, be sure to use unique passwords. Microsoft recommends using at least eight characters. Two-step verification and account activity email alerts can help as well.
And if you're an online shopper, prices that seem too good to be true probably are.
Also, be wary of sellers with a lot of negative reviews and those without any recent reviews.
Amazon has some policies to protect shoppers, too. It waits to pay sellers until it's confident purchases have been delivered. And the company promises a full refund for any purchases that don't arrive or aren't what a customer expected.
An Amazon spokesman told The Wall Street Journal that sellers will be reimbursed for any money lost.
RELATED: Take a look back at the biggest news scandals of last year:
Top scandals of 2016
Top scandals of 2016
Donald Trump & Bill Bush tape
Video obtained by The Washington Post captured President-elect Donald Trump using vulgar terms to brag about groping and kissing woman. The video was from 2005 and Trump was talking to Billy Bush who was an Access Hollywood host at the time. Trump labeled the video "locker room talk".
(Obtained by The Washington Post via Getty Images)
Olympic gold medalist Ryan Lochte claimed that he and three other Team USA swimmers were robbed at gunpoint in Rio by men claiming to be police. Police in Brazil refuted his claims and it was later discovered that he lied about the incident.
(Photo by Matt Hazlett/Getty Images)
DNC email leak
Democratic National Committee Chairwoman Debbie Wasserman Schultz stepped down from her position just before the convention after leaked emails appeared to show party officials favoring Hillary Clinton over Bernie Sanders.
Kanye West was hospitalized for exhaustion after the remaining dates of his Saint Pablo Tour were called off. TMZ reported that he suffered a nervous breakdown that was triggered by the anniversary of his mother's death.
(Photo by Scott Legato/Getty Images)
Former chairman & CEO of Fox News, Roger Ailes, stepped down from his position after the network's former anchor, Gretchen Carlson filed a sexual harassment lawsuit against him. Fox eventually reached a $20 million settlement with Carlson.
(Photo by Frederick M. Brown/Getty Images)
EpiPen maker Mylan
The skyrocketing costs of EpiPen's manufactured by Mylan NV pharmaceutical company was brought to the forefront in 2016. The price of the medication used by allergy sufferers increased by 400% over the past decade.
(REUTERS/Jim Bourg/File Photo)
Anthony Weiner sexting scandal
Former New York congressman Anthony Weiner was embroiled in another sexting scandal in 2016. His wife and top aide to Hillary Clinton, Huma Abedin, announced she would be separating from her husband in August after the new allegations of sexting surfaced.
(Photo by Lars Niki/Corbis via Getty Images)
Wells Fargo Bank
Employees in Wells Fargo's community banking division were accused of opening nearly two million unauthorized accounts to reach sales goals. Wells Fargo was hit with $185 million in fines and thousands of people were fired in connection with the fraud scheme.
(Photo by FG/Bauer-Griffin/GC Images)
Brad Pitt and Angelina Jolie
After two years of marriage and more than a decade together actress Angelina Jolie filed for divorce from Brad Pitt. The actor was investigated on child abuse accusations after an incident on the family's private plane, but he was eventually cleared of any wrongdoing.
(ROBYN BECK/AFP/Getty Images)
Baylor sex assault scandal
An investigation at Baylor University uncovered 17 separate acts of sexual assault by 19 members of the Baylor football team. Coach Art Briles was fired but denies that he was told about the alleged crimes. Other school officials also reportedly knew of the assault accusations and failed to take the appropriate steps to address them.
(Photo by Frank Jansky/Icon Sportswire via Getty Images)
Bill Cosby sex abuse scandal
The scandal surrounding Bill Cosby took a major step forward in 2016 when a judge ruled that the actor must stand trial on sex abuse charges. More than 50 women have come forward claiming that Cosby sexually abused them over the past several decades.
(REUTERS/Matt Rourke/Pool/File Photo)
Russia doping scandal
More than 1,000 Russian athletes are now accused of being involved in a doping program. A report by the World Anti-Doping Agency says that the athletes span across 30 sports. Russia has been stripped of several Olympic medals due to the scandal.
The scandal that started in 2013 came to a head in 2016. New Jersey Governor Chris Christie's top aide, Bridget Kelly and a former Port Authority executive, Bill Baroni were found guilty on all counts in the George Washington Bridge trial. They were accused of intentionally causing a traffic gridlock in Fort Lee during morning rush hour for a week in September 2013.
(Photo by Drew Angerer/Getty Images)
Johnny Depp and Amber Heard
Amber Heard filed for divorce in May and soon after that she also filed for a restraining order against Depp claiming he threw a cellphone at her during a fight. The two reached a multi-million dollar settlement that is supposed to be donated to the ACLU and Children's Hospital of Los Angeles.
CNN severed ties with Interim Chair of the Democratic National Committee and network contributor Donna Brazile after it was revealed that she sent debate questions to Hillary Clinton's camp ahead of the CNN debate.
(SAUL LOEB/AFP/Getty Images)
Reenlistment bonus scandal
Nearly a decade ago the Pentagon was offering soldiers bonuses of $15,000 or more to entice them to reenlist and fight in Iraq and Afghanistan. In 2016, officials were demanding that thousands of those soldiers repay the money because the bonuses were given improperly. Defense Secretary Ash Carter eventually suspended the efforts to take the money back.
(Photo by RJ Sangosti/The Denver Post via Getty Images)
Kanye West and Taylor Swift's phone conversation
In July, Kim Kardashian posted a video of her husband and Taylor Swift discussing the lyrics to Kanye's song, "Famous." Swift had said that she was never made aware of the song's lyrics but many people think the videos that Kim posted on social media show that she did.