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Committee members have made the beaconing allegation before, and Mr. Rogers was challenged about the absence of any detail about the charge in his panel’s report. He said the victims of the beaconing were reluctant to come forward.

“So there isn’t this huge outcry, people wanting to line up at press conferences to talk about material that they’ve had beaconed off of their particular routers,” Mr. Rogers said.

Similarly, the report provides few specifics to back up the committee’s allegations that equipment made by the companies has secret “back doors” that allow unauthorized access to the networks in which they are used.

But at a security conference earlier this year, a well-known “white hat” computer hacker who uses the handle FX demonstrated a series of vulnerabilities in Huawei systems.

“The flaws [he demonstrated] are numerous and [include vulnerabilities to] simple attacks known since the 1990s,” said Ira Victor, a computer forensic specialist for Data Clone Labs who attended the presentation. “These are not flaws that are found in competing vendors.”

The committee report states that, since the firms’ products often include thousands of components and millions of lines of code, it is nearly impossible to ensure their security against deliberate efforts to compromise it by the manufacturers.

The report also states that evidence about unrelated illegal activity concerning sanctions busting, bribery, and labor and immigration law violations has been handed over to the FBI.