Tom Kellermann, a former computer security official at the World Bank who now works at a firm called Core Security Technologies, said the most advanced hackers in the world are increasingly targeting financial institutions, particularly those involved in trading.

WSJ: Hackers Penetrate Nasdaq's Computers

But the largest collections currently available from Core Security Technologies, Immunity and an open source project known as Metasploit include exploits for less than 10% of the 14, 000 security flaws publicly revealed in information technology systems over the last five years.

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