Washington ? Experts can now download a genetic blueprint from the Internet and use mail-order materials to assemble a deadly virus, say researchers who made a synthetic polio virus in the lab to demonstrate the threat.

“The world had better be prepared,” said Dr. Eckard Wimmer, leader of a biomedical research team at the University of New York at Stony Brook where the virus was assembled.

The researchers made the virus in the laboratory using data from the Internet and tailor-made sequences ordered from a laboratory supply service. They injected the virus into mice to show that it worked. The animals were paralyzed and then killed.

“The reason we did it was to prove that it can be done and it now is a reality,” said Wimmer, senior author of a study appearing today in the journal Science.

“This approach has been talked about, but people didn’t take it seriously,” he said. “Now people have to take it seriously.”

Wimmer said the laboratory demonstration proved that eradicating a virus in the wild may not mean it is gone forever. Now, he said, biochemists can reconstruct viruses.

The polio virus assembled in the laboratory is one of the simplest of the human plagues, said Jeronimo Cello, first author of the study.

“It was very easy to do,” he said.

Smallpox and other lethal viruses are much more complex and difficult to assemble, but Cello said, “Probably in the future it would be possible.”

Wimmer said it “would be very difficult now to re-create the smallpox virus, but eventually you would be able to do that.”