WASHINGTON (Reuters) - The U.S. government should abandon an Internet-voting system planned by the Pentagon because hackers could easily tamper with election results, several computer-science professors said on Wednesday.

Military personnel and other U.S. citizens located overseas will be able to cast their ballots online for some primary and general elections this year under the Defense Department's Secure Electronic Registration and Voting Experiment, rather than casting absentee ballots by mail.

But their votes could be vulnerable to a range of cyber attacks that have already rocked banks, Internet providers and other businesses that operate online, said four researchers who serve on an advisory panel for the program.

Hackers could knock vote-tallying computers offline with a flood of data in "denial of service" attacks; set up phony Web pages to intercept or alter votes; or spread a virus to participants' computers to monitor or alter their voters, the researchers said.

"Because the danger of successful large-scale attacks is so great, we reluctantly recommend shutting down the development of SERVE and not attempting anything like it in the future until both the Internet and the world's home-computer infrastructure have been fundamentally redesigned, or some other unforeseen security breakthroughs appear," they said.

The Pentagon has no intention of shutting down the program, a spokesman said. "Security is enhanced, procedures are in place. I don't know them all and I wouldn't share them if I did," said Defense Department spokesman Glenn Flood.

Flood noted the four researchers who authored the report were not joined by the six other experts who served on the advisory panel.

The report was written by Johns Hopkins professor Avi Rubin; University of California professor David Wagner; David Jefferson, a computer scientist at the Livermore National Laboratory; and computer consultant Barbara Simons.