Toshiba Corp. has announced it might have to revise operating profit downward by just over ¥50 billion ($412 million) for the three years through March 2014 because of an in-house investigation into improper accounting at its infrastructure-related businesses.

The estimate, contained in a statement the company issued late Wednesday, compares with about ¥695 billion in operating profit reported over the period. It was the first hint about the potential impact the accounting problem might have since the electronics conglomerate withdrew its earnings forecasts last week and warned it may have to revise earnings.

Toshiba might form a panel of outside experts versed in legal affairs and accounting to conduct a detailed probe into the matter as early as this week. The probe might come up with a different estimate for a revision, the company said.

On Friday, Toshiba withdrew its projections for consolidated earnings for the year ending March 2015, citing accounting irregularities. It is expected to release fiscal 2014 results as early as June.

The in-house investigation centered on three divisions in the company that were involved in infrastructure projects dealing with electricity generation, transportation and other areas. It found cases where project costs were underestimated or reserves against losses were not posted correctly, according to the company.

The outside panel’s probe could extend to consolidated subsidiaries.

Toshiba shares plunged 17 percent Monday after the company announced it was suspending its earnings forecast and canceling a dividend. Wednesday’s announcement of the ¥50 billion cut to earnings caused a rebound Thursday after easing market concerns about the size of the impact.

“Toshiba’s annual operating profit exceeds ¥300 billion, compared with that, the damage from improper accounting is rather small,” said Hideki Yasuda, an analyst at Ace Research Institute in Tokyo. “That still doesn’t change the fact that there were problems, however limited, and that investor trust was betrayed. This loss of faith is likely to result in a discount on Toshiba relative industry peers.”

“It’s good to finally get some sense of the scope of the problem,” said Yasuaki Kogure, chief investment officer at SBI Asset Management Co. “Without any information it was possible to imagine the loss swelling to hundreds of billions of yen.”