Six years after arresting turncoat Robert Hanssen, the FBI remains vulnerable to espionage from within, the parent Justice Department said in a report Monday.

The reason for this, said the Justice's Office of Inspector General, is that the bureau has failed to fully adopt security measures to track suspicious behavior involving its own employees.

The investigation by the IG's office sought to examine the extent of internal security at the nation's lead law enforcement and domestic spy agency following the 2001 capture of Hanssen, who admitted spying for Moscow for cash and diamonds over two decades.

The 41-page unclassified report credits the FBI for taking at least two critical steps to crack down on internal spies — creating a new unit designed specifically to detect security penetrations within the agency and installing senior operational posts in its counterespionage section. These posts were filled with representatives from the CIA or elsewhere in the intelligence community to ensure "impartiality and an objective evaluation of source information."

Such measures, proposed by the IG in 2003, were initially resisted by the FBI.

However, the internal investigation found that the FBI had yet to put in place internal monitoring procedures other recommendations by the IG — such as creating a central repository to collect and analyze bizarre or otherwise derogatory information — concerning FBI employees.

The report also found that the FBI's program to review suspicious employees periodically over their years of service also remained spotty because it hadn't created full case files on them. This was due at least in part to faulty technology, it said.

As a result, such gaps expose the nation to internal spy threats and could have been to blame for security breaches by FBI intelligence analyst Leandro Aragoncillo, who was arrested in October 2005. He was later sentenced to 10 years in prison for passing secret U.S. documents in an effort to topple the Philippine government.

"The circumstances surrounding Aragoncillo's activities and the FBI's response to them are stark reminders of the vulnerabilities that persist within the FBI's security program and the need to address these vulnerabilities," states the report by Inspector General Glenn A. Fine, which called the security failures unacceptable.

"We believe the FBI must be vigilant in attempting to deter and detect the internal penetrations that have occurred in the past and that may occur in the future," the report said.

Responding, FBI assistant director John Miller said he appreciated the IG report, noting that it had found the bureau had made significant progress in several areas. He said the agency fully intended to implement the remaining security measures, but did not indicate a timeframe.

"We will continue to work with the OIG to make additional progress toward implementing these recommendations and in our efforts regarding espionage activities on the whole," Miller said.