The many Bernard Madoff investors who withdrew money from their accounts over the years are now wrestling with an ethical and legal quandary.

What they thought were profits was likely money stolen from other clients in what prosecutors are calling the largest Ponzi scheme in history. Now, they are confronting the possibility they may have to pay some of it back.

The issue came to the forefront this week as about 8,000 former Madoff clients began to receive letters inviting them to apply for up to $500,000 in aid from the Securities Investor Protection Corp.

Lawyers for investors have been warning clients to do some tough math before they apply for any funds set aside for the victims, and figure out whether they were a winner or loser in the scheme.

Hundreds and maybe thousands of investors in Madoff’s funds have been withdrawing money from their accounts for many years. In many cases, those investors have withdrawn far more than their principal investment.

“I had a call yesterday from a guy who said, ‘I’ve taken out more money then I originally put in, but I still had $1 million left with Madoff.

Should I file a $1 million claim?’” said Steven Caruso, a New York attorney specializing in securities and investment fraud. “I’m hard-pressed to give advice in that situation,” Caruso said.

Among the options: Get in line with other victims looking for restitution. Keep quiet and hope nobody notices. Return the money. Or hire a lawyer and fight to keep profits that were probably fraudulent.

No one knows yet how many people will emerge as net winners in the scandal, but the numbers appear to be substantial.

Many of Madoff’s long-term investors have, over time, cashed out millions of dollars of their supposed profits, which routinely amounted to 11 percent to 15 percent per year.

Jonathan Levitt, a New Jersey attorney who represents several former Madoff clients, said more than half of the victims who called his office looking for help have turned out to be people whose long-term profits exceeded their principal investment.

“There are a lot of net winners,” he said.

Asked for an example, Levitt said one caller, whom he declined to name, invested $1.8 million with Madoff more than a decade ago, then cashed out nearly $3 million worth of “profits” as the years went by.

On paper, he still had $4 million invested with Madoff when the scheme collapsed, but it now looks as if that figure was almost entirely comprised of fictitious profits on investments that were never actually made, leaving his claim to be owed anything unclear.