WASHINGTON (Reuters) - Computer spying and theft of personal information have risen notably in the past year, costing tens of millions of dollars and threatening U.S. security, the FBI's cyber division head said on Wednesday.

FBI Assistant Director Shawn Henry told reporters that organized-crime groups are drawn by the ease of reaching millions of potential victims.

He said as many as two dozen countries have taken an "aggressive interest" in penetrating the networks of U.S. companies and government agencies.

He declined to specify countries, but U.S. intelligence agencies have voiced concern over Russia and China's abilities to electronically spy on the United States and disrupt U.S. computer networks.

As one possible example of Russia's electronic spying prowess, Georgia accused Moscow in August of conducting "cyber warfare" to shut down Georgian government websites at the same time as it carried out a military offensive.

U.S. federal agents are stepping up efforts to fight computer crime, and working with foreign counterparts where the rising wave of computer attacks has awakened international interest, Henry said.

"Over the past year the malicious activity has become much more prevalent," Henry said. "The threat continues to increase."

An attack method growing in popularity is "botnets," in which malicious software spreads via viruses to computers of unwitting individuals and companies forms networks that can then be used for data theft or shutting down a system, Henry said.

Another method, "Spearfishing," when hackers get a copy of a company's e-mail list, then send out official-looking requests for employee personal information, has also been a growing problem, he said.

He said computer crime has invaded Wall Street, but had nothing to do with the current financial system crises.

Individual investment companies have, however, lost tens of millions of dollars through "pump and dump" schemes in which criminals penetrated multiple client accounts and used them to run up the price of low-liquidity stocks and dump them from their own accounts.

Internet Crime Complaint Center, which the FBI helps run, has recorded more than 1 million complaints since its founding in 2000 and numbers are now running about 18,000 to 20,000 per month, Henry said.

(Editing by Philip Barbara)

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