Investigators say they do not know the extent of significant hacks inside the government and its background check contractors, because the Office of Personnel Management and the companies did not have sufficient computer logs.

This is the reason so many questions remain, a year after data breaches were discovered at OPM, KeyPoint Government Solutions and USIS.

Tracking everyday network traffic requires an investment and some managers decide the expense outweighs the risk of a breach going undetected, security experts say.

In this case, taking chances has delayed a probe into the exposure of secrets on potentially 18 million national security personnel.

Last summer, OPM learned from outsiders at the Department of Homeland Security it had been hacked starting in November 2013. Manuals about OPM IT assets stolen at the time "would give you enough information that you could learn about the platform, the infrastructure of our system," said OPM Chief Information Officer Donna Seymour, assenting that they could serve as a blueprint for attackers.

Seymour and representatives from the other hacked organizations were testifying before the House Oversight and Government Reform Committee on Wednesday.

It is unclear whether this episode or another breach at KeyPoint provided intelligence that aided the perpetrators behind a second, graver OPM intrusion, which was divulged earlier this month.

Attackers penetrated KeyPoint’s own networks between fall 2013 and August 2014. DHS still is not able to determine how the bad actors broke into the company's systems.

A KeyPoint employee’s login was stolen to snatch personal details in OPM systems on nearly all federal employees and anyone who has ever seen classified information, a company official acknowledged.

But, "we have seen no evidence of a connection between the incursion at KeyPoint and the OPM breach that is the subject of this hearing,” Keypoint President and CEO Eric Hess testified.

A committee aide told Nextgov forensics experts found no evidence because KeyPoint had never set up logs.

"In other words, they don't know what happened," the staffer said. "It's like if you go into a 7-Eleven and the security camera is not on."

The cyberspies somehow deployed a certain type of malware capable of traversing KeyPoint’s network, said Ann Barron-DiCamillo, director of the DHS U.S. Computer Emergency Readiness Team.

"They entered the network -- we're not quite sure how because of lack of logging," she said at the hearing. About 27,000 employee records were potentially exposed, according to DHS.

The intruders, suspected to be Chinese-sponsored spies in each attack, walked out with a whole lot more during the most recent breach of OPM personnel files.

The malicious operation consisted of two hacks. One scored Social Security numbers and other identity information on 4.2 million current and former government workers. The other involved an OPM background investigation system that stores private dossiers on employees approved to see classified information, including habits, family relationships and foreign contacts. That incident reportedly could expose around 18 million individuals, a figure, according to OPM, derived from the number of Social Security numbers held in the database.

At USIS, personal information on "some 31,387 individuals who were potentially subjects of background investigations work" may have been compromised, according to a June 22 letter from company representatives to committee Ranking Democrat Rep. Elijah Cummings, D-Md., that Nextgov obtained.

Homeland Security also was unable to find the initial point of entry “because of the lack of logging," said Barron-DiCamillo. The company reported to the government hacker activity began in December 2013 and was last observed July 4, 2014.

For the first time, USIS also disclosed, in the letter, that some work performed for agencies besides OPM may have been affected, including investigations on employees at the National Geospatial-Intelligence Agency, Immigration and Customs Enforcement, and the U.S. Capitol Police.

OPM apparently lacked logs too. The most recent event began in June 2014 and was not identified until April. The federal government still does not know the extent of the intrusion, as of June 24, 2015.

"We had put the tools on our network just over the last six months or so to be able to see this type of activity in our network," Seymour said. Officials could go back in time to track "this latent activity that went back to even prior to my arrival at OPM," in 2013.

Depending on the quality of the analytical tools, they can be pricey, so organizations in general must decide whether to pay for technology or take a gamble.

"There's millions of net-flow records that happen” each day and “that does require quite a bit of storage," Barron-DiCamillo said.

Lawmakers on both sides of the aisle aired disappointment with the performance of the current OPM administration.

Addressing agency Director Katherine Archuleta in particular, Rep. Mark DeSaulnier, D-Calif., said, "You appear to come across as petulant, defensive and evasive."

Archuleta said her emotions were being misconstrued.

"I just take very, very seriously what has happened," she said. "I do feel passionate about what has happened."

To that, DeSaulnier replied, "Sometimes, you can feel passionate about things but not be capable of doing what you desire to do."