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NYSE Website Targeted by Cyber Attack; Shares Fall

NYSE Euronext said Wednesday its public Web site, NYSE.com, was the target of a cyber attack, according to authorities.

"NYSE Euronext has been informed by authorities that its public Website, NYSE.com, has been the subject of a 'denial of service' attack. To date, NYSE.com has not experienced any impact, which may be the result of its security design," the company said.

The incident has not and could not impact the trading and data systems of NYSE Euronext markets, which operate on private networks, the company said.

However, shares of NYSE Euronext shares hit session lows, falling about 5 percent on the news.

The company said it is continuing to work with authorities.

The cyber attack on the exchange's Web site follows several technology-related incidents at the exchange last week. Among these incidents was an erroneous notice of delisting for American International Group and an issue with the trading systems that required trading to be extended by 15 minutes last Thursday.

CNBC contacted other exchanges and did not hear of any similar problems. Both CME Group and Nasdaq said they did not have a problem, and a spokesperson at NYMEX was not immediately available.