It’s only been five-and-a-half years since Bernie Madoff’s $50-billionaire dollar Ponzi scheme was exposed, but many investors—especially younger ones—don’t know about the giant scam that left victims penniless.

When it comes to preventing history from repeating itself, knowledge is key.

“The least likely group ( 18 to 29 year olds)  to know about one of the biggest frauds aren’t seeking any investment advice,” says Brian Fox, president of Confirmation.com, which conducted a survey of nearly 1,000 investors to get a sense of their familiarity with the scheme that landed Madoff in prison for 150 years. “That speaks to building the case that we will see history repeat itself.”

According to the survey, about one-third of respondents between the ages of 30 and 44 didn’t know who Madoff is, while close to half of respondents age 18 to 29 couldn’t make the identification. Nearly one-third of people between the ages of 45 to 60 didn’t know his identity. On the flip side, 80% of people over the age of 60 could name Madoff as the mastermind of the biggest Ponzi scheme in modern history.

To help inform investors—particularly those in the Millennial generation—there are telltale signs to look for to prevent becoming a fraud victim.  Here’s are investment advisors top three red flags: 

Red Flag No.1: Money Manager and Custodian are One in Same

One of the reasons Madoff was able to get away with his fraud for so many years is because he held people’s money at his firm instead of with an independent custodian.

“The most important thing to understand is who is going to hold your money,” says Bob Phillips, managing principal at Spectrum Management Group. “Scams tend to be perpetrated by people who pitch you the investment idea and then control your money.”

Money managers recommend investors only put their money with a firm that uses an independent custodian to hold the funds.  An independent custodian provides investors  a monthly or quarterly statement from both the investment firm and the custodian.  If the numbers don’t match, that’s a bad sign.

Red Flag No.2: Returns Outpace by Large Margin

The adage of “if it sounds too good to be true, it is” especially rings true in the investing world.

The allure of getting rich quick can be very powerful, but it can also be a sign something is amiss.

“You want to ask yourself: ‘Does this make sense? Does this look right if you give it the sniff test?’” says Fox. “Do the returns seem abnormally high over an extended period?”

Comparing returns is easy online and if a search doesn’t show any results for a fund—that is a pointer the investment idea may not be legitimate.

People who want to test a not-well-documented investment idea a go, should get a third party involved, advises Dan Cuprill, co-founder and managing partner of Matson & Cuprill.

“If you have doubts, don’t proceed or hire another professional for an independent analysis,” says Cuprill. By law, certified financial planners have a fiduciary responsibility to put the client first and that is a good starting point, he says.

Red Flag No.3: The Investment Professional is Overly Flashy

Many Madoff victims happily turned over their money to him without asking any  questions because he had formed a well-established reputation and created a feeling of exclusivity when it came to investing with him.

“He was successful largely because he had such a reputation that nobody thought to question him,” says Cuprill. “But when you looked at his returns he was producing 9%, 10%, 11% no matter what the markets did.” He says investors have to look at money managers as people and not rock stars to prevent themselves from being awed and thus drawn into a scam.

“There are no gurus in investing,” says Cuprill. “Anyone who tells you what the market is doing is lying to you. You have to be skeptical.”