Police in the US city of Boston are investigating a major American media corporation for causing a security alert that closed bridges and roads.
The electronic devices were meant to advertise a cartoon
Turner Broadcasting System placed electronic devices with blinking lights around the city as part of a campaign to market a late-night TV cartoon.
Police were called out to investigate the suspicious-looking devices, which disrupted road and rail traffic.
Two men who placed the objects have been charged, state officials said.
Peter Berdovsky, 27, and Sean Stevens, 28, were each charged with placing a hoax device and disorderly conduct, Attorney General Martha Coakley said.
Turner Broadcasting System has apologised for the scare.
The small electronic sign-boards were placed near roads and under bridges over the Charles River, prompting suspicion from commuters.
A police bomb squad blew up one of the marketing devices
Police destroyed the first package they found to see if it contained explosives.
Parts of the subway, a bus station and a major highway were among areas shut down as police investigated reports of suspicious devices.
Turner said that the packages in question were "magnetic lights that pose no danger".
They were designed to promote an adult-oriented cartoon called Aqua Teen Hunger Force.
In a statement, the corporation said the campaign had already been in place in 10 US cities, including Boston, for several weeks.
"We regret that they were mistakenly thought to pose any danger," the company said.
Authorities in Boston say they are considering charges against Turner and an advertising company, and could demand financial compensation for the massive disruption caused by the marketing campaign gone wrong.
"We're not going to let this go without looking at the further roots of how this happened to cause the panic in this city," Ms Coakley told a news conference.
The two men who have been charged face up to five years in prison.