Computer hackers who infiltrated House computers in late 2006 compromised as many as 50 machines throughout the chamber, according to a memorandum prepared by the Information Systems Security Office.

As stated in the confidential document, a copy of which was obtained by Roll Call, cyberspies infiltrated computers in 15 offices, including eight committee offices and seven personal offices.

In addition to Reps. Frank Wolf (R-Va.), Mark Kirk (R-Ill.) and Chris Smith (R-N.J.), who acknowledged the incident last month, hackers accessed machines in the offices of the late Reps. Tom Lantos (D-Calif.) and Henry Hyde (R-Ill.), and Reps. Mike Pence (R-Ind.), Steve Chabot (R-Ohio), now-Sen. Sherrod Brown (D-Ohio) and Del. Eni Faleomavaega (D-American Samoa).

The slide-show-style memorandum also lists computers or servers compromised in the Education and Workforce, Commerce, International Relations, Transportation and Infrastructure, Homeland Security and Ways and Means panels. The document also listed one server violated in the office of the Congressional-Executive Commission on the People’s Republic of China.

The International Relations Committee, since renamed the Foreign Affairs Committee, suffered the largest attack, with 25 computers and one server infiltrated, the memo notes.

According to the report, the first compromised computer was detected in October 2006 — although it does not indicate in which office — and the FBI was contacted to assist in the investigation. Using information gleaned from that computer, analysts conducted a subsequent scan of the “House Network” and found additional infected machines.

The report states that the hackers were able to copy files and record keystrokes from infected machines, which were accessed through Web sites, active content in e-mail messages and instant messaging.

A spokesman for the Office of the Chief Administrative Officer, which oversees the Information Systems Security Office, declined to comment on any aspect of the incidents or investigations.

Although House Administration Chairman Robert Brady (D-Pa.) called on the CAO in early June to work with the FBI and “adopt all necessary protections for House information,” it remains unclear whether or how much the chamber has improved its technological security since the attacks were discovered.

While House Information Resources, the chamber’s information technology office, issues minimum standards for Member offices, each office sets its own policies regarding technology, including the purchase of its computer equipment from office funds.

An FBI spokeswoman declined to comment Wednesday and would not confirm whether the investigation remains open.

Although the House report does not identify the source of the attacks, Wolf asserted in June that the invasion originated from China.

“In subsequent meetings with House Information Resources and FBI officials, it was revealed that the outside sources responsible for this attack came from within the People’s Republic of China,” Wolf said in a statement. The Virginia lawmaker said his computers were accessed in August 2006. “These cyber attacks permitted the source to probe our computers to evaluate our system’s defenses, and to view and copy information. My suspicion is that I was targeted by Chinese sources because of my long history of speaking out about China’s abysmal human rights record.”

Chinese officials have denied those accusations.