Baruch Israel Hertz learned the hard way that practising what you preach has its down side. The chief executive of a US online trading company was forced to liquidate almost half his stake in the company this week after facing margin calls of $45m (£28.4m).

Mr Hertz, the head of Track Data, a financial information and trading firm, stacked up the losses during last week's 25% decline in Nasdaq. The margin calls from four different brokerage firms are understood to add up to one of the biggest made for an individual on Wall Street.

Track Data has been one of the most aggressive advertisers for online trading in recent years. Mr Hertz himself appears on the company website to push "myTrack", its online trading service, by proclaiming: "You don't have to be a pro to trade like one."

Mr Hertz was unavailable for comment yesterday but Rafi Reguer, the company's marketing director, said that the company had not been involved in the margin calls.

The trading in "several large companies" was carried out in Mr Hertz's own account, he said. "The debt is entirely his own, and not an obligation of Track Data."