The blast shattered a thick, wall-sized window lining a ground-floor corridor and damaged furniture, books and bookcases inside the building, but no workers were injured, according to police Sergeant Nick Muyo.

There were approximately 45 PayPal employees working in the four-storey building at the time, Muyo said.

"We were lucky no one was hurt," he told AFP, adding: "It doesn't appear anyone was targeted."

The Internet auction website eBay, which bought the PayPal online financial transactions service in 2002, said the company had received no threats prior to the blast.

"There was no warning," Muyo said. "Everyone is completely surprised by this thing. You have to consider the fact it was Halloween and it could have been a Halloween prank, but I don't want to speculate."

The device was apparently placed on a ledge at the outer base of a window near a breezeway easily accessible from a parking lot.

The explosion did not affect PayPal operations, aside from prompting the company to have the 1,900 employees based there work from home on Wednesday, according to spokeswoman Amanda Pires.

"We asked people at the campus to work from home today as a precaution," Pires told AFP. "We are working with federal and local law enforcement right now to find out what happened.

"We believe it was an isolated incident," she said.

Police were hoping surveillance camera recordings from the building would help them solve the case.

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