NEW YORK (AP) -- Shares of Aflac Inc. hit their lowest point in nearly nine years Monday after an analyst downgraded the insurance company based on its exposure to risky hybrid securities issued by European financial firms.

Deutsche Bank analyst Darin Arita on Monday cut his rating on the Columbus, Ga.-based company to "Hold" from "Buy," expressing concern about the value of hybrid securities -- or instruments with both debt and equity features -- that Aflac holds.

The stock fell $4.87, or 20 percent, to end at $19.62, with volume spiking to nearly five times average daily trading. Earlier, the stock touched $19.35, the lowest point shares have changed hands since March 2000.

Aflac shares started the day down 46 percent since the beginning of the year. The stock dived last week after another analyst warned about possible securities-related losses. Also, late Friday Aflac received a downgrade from Standard & Poor's credit ratings agency.

The S&P downgrade just a half hour before the close of Friday's session, and was likely also weighing on the stock in Monday trading. FBR Capital Markets analyst Randy Binner said the S&P cut came as a surprise, given that Aflac has not yet reported its fourth-quarter and full year results.

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