Because the first exchange-traded funds to hit the market were based on mainstream indexes, they offered relatively safe investments, but with new ETFs tracking increasingly narrower slices of the equity, commodity and currency markets, that is no longer the case, the Philadelphia Inquirer reports.

Today, there are 350 ETFs, with 40 of them created just in the last year.

Should recent reports be true that the Securities and Exchange Commission is about to approve the first actively managed ETF, that would be an even riskier variety.

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