The Securities and Exchange Commission (SEC) said unknown traders earned $1.7 million in profits through "irregular and highly suspicious" options trades on Heinz shares booked on Wednesday, one day before the announcement that Berkshire and 3G were acquiring Heinz in a $28-billion deal.
The SEC said it believed the traders had knowledge of the takeover ahead of the announcement early Thursday morning in New York.
The trades were "a serious red flag that traders may be improperly acting on confidential nonpublic information," said SEC enforcement official Daniel Hawke in a statement.
The acquisition announcement sent Heinz shares up nearly 20 percent from $60.8 per share to $72.50, the takeover offer price.
The value of the specific call options traded from the Swiss account jumped 1,700 percent in the same time frame, the SEC said.
Among the red flags cited by the SEC: the Swiss account had engaged in no trading of Heinz securities since September 1, 2012.
The SEC said freezing the account would prevent any profits from being withdrawn and force the unknown traders to come forward.
"Despite the obvious logistical challenges of investigating trades involving offshore accounts, we moved swiftly to locate and freeze the assets of these suspicious traders," said Sanjay Wadhwa, senior associate director of the SEC's New York regional office in a statement.
The traders "now have to make an appearance in court to explain their trading if they want their assets unfrozen."