A company whose e-voting machines have come under fire from election officials in New Jersey confirmed that its site had been hacked Thursday.

A section of Sequoia's Web site was hacked overnight, and when the company realized what had happened it took the site down and removed the "intrusive content," Sequoia spokeswoman Michelle Shafer said.

Sequoia made "security enhancements" to protect the site from further hacking, and it was back online Thursday afternoon, Shafer said. The company is investigating the origin of the attack.

The hack was noticed Thursday morning by Ed Felten, a computer scientist who has been asked to investigate voting-machine discrepancies in the state's primary election.

The "Ballot Blog" page of Sequoia's Web site had no content early Thursday afternoon Eastern Time, and earlier in the day, there were messages on the page announcing that it had been hacked, Felten told IDG News Service.

Felten, a Princeton computer science professor and a critic of e-voting systems, had been asked by a group representing New Jersey county clerks to examine Sequoia machines used in a Feb. 5 New Jersey presidential primary election.

In his e-mail, Felten said that at around 6:30 a.m. Eastern Time, the Ballot Blog, in which Sequoia gave an in-depth explanation of what had gone wrong in New Jersey, had been replaced with a message saying it had been hacked. He said the message named those who were responsible for the hack, but he could not remember what that name was other than "it was a mixture of lower-case letters and numbers."

By mid-morning, the site had been taken offline by its Web-hosting provider and redirected to a hosting-provider page that said the page had been suspended temporarily for maintenance.

Sequoia has come under scrutiny for discrepancies in the voting tallies generated by approximately 60 of the state's Sequoia Voting Systems AVC Advantage e-voting machines during last month's election. On Wednesday, a group representing clerks from a half-dozen New Jersey counties wrote to State Attorney General Anne Milgram asking her to investigate the problems.

In most cases, the discrepancy involved a one- or two-vote difference between the paper tape logged by the machine and the number of votes stored in the machine's memory cartridges. Sequoia blamed the discrepancy on poll worker error and said the problem could be fixed with a software update, but state clerks requested a third-party investigation.

Last Tuesday, the clerks group asked Felten to examine the Sequoia machines. However, Sequoia threatened legal action against Felten, saying that such a review would violate the company's licensing agreement, so he did not carry out his investigation.

(Robert McMillan in San Francisco contributed to this article.)

This story was updated on March 20, 2008