Amcore Financial Inc. has amended its shareholder rights plan, adopting new measures that will make it much harder for a hostile suitor to buy the company.

Under the new plan, "poison pill" provisions take effect when an investor acquires 15% of the company's common shares. The trigger can be reduced to 10% if the board declares an investor holding that much stock to be an "adverse person."

The old plan, which was due to expire today, was designed to take effect when an investor acquired 50% of the company's shares.

The plan was amended because of its impending expiration, and not because of any outside event, a company spokesman said.

"The new rights plan, like the existing rights plan, is intended to promote continuity and stability, deter coercive or partial offers which will not provide fair value to all shareholders, and enhance the board of directors' ability to represent all shareholders and thereby maximize shareholder values," said Robert J. Meuleman, Amcore's president and chief executive officer.

Amcore is a $2.4 billion-asset banking company in northern Illinois.

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