The targeted attacks on Google and more than 30 other U.S. companies late last year bear striking similarities to targeted attacks on 100 U.S. companies last summer, a security researcher familiar with the attacks said Tuesday.

Last July, workers at about 100 U.S. technology companies were targeted with e-mails containing malicious PDF files that exploited a zero-day vulnerability in Adobe Reader. The attacks were detected early and there were no serious consequences, said Eli Jellenc, head of international cyberintelligence at VeriSign iDefense.

In mid-December, Google, Adobe Systems, and a host of other Silicon Valley companies were targeted by attacks originating in China, prompting Google on Tuesday to say that it will stop censoring its Chinese search results and to threaten to pull out of that market. The latest attacks also involved malicious PDF files in e-mail attachments and the code was similar to the previous attack, Jellenc said.

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