The 2020 Census is at risk of being manipulated by bad actors online, a top official from the Government Accountability Office told the Senate Homeland Security and Governmental Affairs Committee on Tuesday.

Worries about a skewed population count come in a year in which the Commerce Department, the agency which oversees the Census Bureau, has already announced a need to increase the overall “end of project” cost of the 2020 census by more than $3.3 billion.

Eugene Dodaro, Comptroller General of the Government Accountability Office, said his office believes the Census is one of the “highest management risks” for projects currently underway in the federal government. He said the bureau continues to be plagued by leadership, staffing, technical, and computer security issues as the ramp up to the 2020 count.

“In addition to the costs, I’m concerned about the security of the IT systems, particularly with the use of the Internet response,” Dodaro testified. “We have the potential for people to misuse the Internet response rate to potentially make the count be, potentially skewed, or there could be other mischief.”

As the Internet has become ubiquitous in American society in the years since the 2010 Census, officials have been aiming to use it to enable a faster response to the questionnaire from some citizens, and officials are hoping it could contain other costs as well. But those aims bring a wealth of challenges.

For example, Dodaro pointed to, “difficulties – significant ones that they've had — securing IT systems.”

“As of last August, for example, only four of the 43 systems that they’re planning to use had completed development and testing,” he said. Dodaro pointed out that security testing was critical because about 75 percent of the IT systems used by the bureau would need to contain “sensitive information that needs to be safeguarded.”

But he also noted that the bureau will need tough congressional oversight in the next 18 months, “because that’s the window that you have to lock down the procedures for the 2020 Census, otherwise it’ll be too late.”

Even though the Commerce Department has had the increased budget figures out for several months, Dodaro said they still haven’t received enough documentation for the GAO to be fully confident in the budget.

To fix these issues, Dodaro said the Census Bureau needed “sustained leadership attention,” but that has been another issue dogging the bureau.

Earlier this year, Census Director John Thompson resigned, leaving a leadership void at the bureau at a critical junction. Commerce Secretary Wilbur Ross told the committee that the first choice to replace Thompson ended up having vetting issues, and so the search for a replacement had to start over from scratch.

Getting an accurate count of the U.S. population is always a huge task with large stakes. The final tally of a Census decides the number of representatives each state has in the U.S. House of Representatives, and also is used as an aid to decide funding on hundreds if not thousands of issues decided by Congress and state and local officials.

Ross said the Census helps decide “hundreds of billions of dollars of federal funding.”

With the new price tag of $15.6 billion for the entire project, the Commerce Department built in “$1.2 billion in contingency funding for known and unknown risks,” Ross said.

“A 10 percent contingency is commonplace for complex private sector projects,” Ross told the committee in his opening statements. “Government tends not to set up reserves, instead funding overruns through subsequent appropriation requests.”