Published: Dec 10, 2010 8:51 PM EST
Updated: Dec 10, 2010 5:51 PM EST

LONDON (AP) - Supporters of WikiLeaks may not be done targeting individuals and businesses they see as their enemies. They've been downloading increasing amounts of the spam-shooting software that can be used in their attacks.

There are fears that the attacks could challenge some Internet giants like PayPal and Amazon.com during the Christmas shopping season.

A data security company says thousands of new downloads of the hostile software were reported overnight.

The software is part of a campaign of revenge against sites believed to have betrayed WikiLeaks, the group that has published hundreds of thousands of secret U.S. diplomatic cables and military intelligence reports.

Users who download the software essentially volunteer their computers to be used as weapons that send streams of electronic spam at targeted websites.

Already, attacks aimed at the main pages of Visa and MasterCard succeeded in making them inaccessible.

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