Bangalore, May 6: An email has threatened Wipro with a biological attack if the Bangalore-headquartered infotech major fails to pay the mailer Rs 500 crore in bitcoins by May 25.

Police sources said the Friday morning mail had threatened the use of the poison ricin through the food served in Wipro's cafeteria or via the toilet seats and toilet paper in the complex. Alternatively, it said, the poison might be scattered from drones.

Ricin is found in the seeds of the castor oil plant and can kill through ingestion or inhalation.

Officers said the mailer had threatened to dispatch a sample dose, claiming to have isolated the toxin and already tried it on stray dogs.

The police have asked their cyber cell to trace the sender of the email. Officers did not rule out a hoax by a prankster, but said that a case had been registered. Either way, they said, investigations would continue and Wipro offices in the city would be placed under additional vigil.

In a statement issued tonight, Wipro said it had taken adequate safety measures.

"Wipro confirms that it has filed a complaint with the local law-enforcement authorities after receiving a threatening letter from an unidentified source," the statement said.

"Wipro has augmented security measures at all its office locations. There is no impact on the company's operations. We have no further comments as the investigation is ongoing."

That the ransom has been sought in bitcoins indicates the mailer is tech-savvy. A bitcoin is a digital currency transacted through a software-based payment system that is accepted worldwide and is run by private agencies.

Although no country has certified bitcoins as legal tender, many tech-proficient people use them for payments since the transactions carry no fees, unlike those made via banking channels or cards. At 10.10pm this evening, a bitcoin was worth over Rs 101,600.

In July 2013, the Sarjapur police station in Bangalore had received an anonymous handwritten letter that threatened to blow up all the Wipro offices within its area. But the letter turned out to be a hoax.

All major information technology companies in the city, including Infosys, Wipro and Cognizant, are protected by paramilitary forces. The local police stations keep a close watch on the neighbourhoods of these companies, which employ thousands of professionals.