A suspicious letter received at Microsoft offices in Reno has shown traces of anthrax after being tested for a third time, Gov. Kenny Guinn said Saturday.

The letter, apparently sent from Malaysia, initially tested positive for the bacterium, but when evaluated for a second time tested negative. State officials will send the letter to the Centers for Disease Control and Prevention for further testing, Guinn said.

Public health investigators were contacting Microsoft employees to determine who might have handled the letter, which contained pornographic material. Thus far, no one has become sick or been diagnosed with the disease.

"This is a very, very low risk to public health," Guinn said.

Microsoft officials alerted health officials Wednesday about the letter, which had been sent to the Microsoft Licensing Inc. office.

Meanwhile, New Yorkers were seeking answers to bioterrorism fears in hospital emergency rooms after an employee at NBC was infected with anthrax.

Authorities originally believed the infected woman, Erin O'Connor, contracted the bacterium by opening a letter containing a powdery white substance, postmarked Sept. 20 from St. Petersburg, Fla.  According to Mayor Giuliani, however, authorities have discovered another letter she opened postmarked Sept. 18 from Trenton, N.J., on which anthrax was detected. The letter dated Sept. 20 has tested negative for anthrax.

Health officials said the infection was an isolated case and stressed there was no cause for alarm. There was no link to terrorism or the inhaled form of anthrax that killed a Florida man last week.

Another letter containing an unknown powder that arrived Friday at the offices of The New York Times was postmarked from St. Petersburg, Fla., and had similar handwriting to the letter received at NBC, said Barry Mawn, head of the FBI office in New York.

On Saturday, however, the Times reported that no anthrax was detected on the envelope after an initial test conducted by the New York City Department of Health. Results from additional tests by the Centers for Disease Control and Prevention are not expected until Tuesday, according to Times spokeswoman Catherine Mathis.

The letter opened by O'Connor, a personal assistant to NBC anchorman Tom Brokaw, was addressed to her boss. 

NBC notified the FBI about the letter the same day it was received. Bureau investigators responded the next day, but did not immediately submit the letter for testing, Mawn said.

"That, unfortunately, did not take place," he said. Bureau investigators wanted to speak with O'Connor before submitting the letter for tests, he said, but could not reach her immediately. Mawn did not provide any other details.

O'Connor noticed a dark-colored lesion three days after the letter was received; on Oct. 1, she began taking the antibiotic Cipro. When the lesion started developing characteristics of anthrax, "a very alert and astute clinician" ordered skin tests, said David Fleming, deputy director for the Centers for Disease Control and Prevention.

After she saw the doctor and began receiving treatment, the FBI was separately notified about the NBC case by the city's health department and submitted the letter for testing, Mawn said.

The results of O'Connor's skin test came back Friday; further tests on the envelope and its contents were still under way.

Officials said they expect O'Connor will recover quickly.

However, reports Friday of the nation's fourth anthrax case since the Sept. 11 terrorist attacks sent New Yorkers scurrying to hospitals in search of anthrax tests and antibiotics. They crowded into the emergency room at St. Vincent's Hospital, wanting to know whether their sore throats and runny noses were symptoms, spokesman William McCann said.

"New Yorkers are nervous about terrorism at this point, and for good reason," McCann said. "I think people heard the word 'anthrax' and panic followed, but there's no reason to panic."

Panic spread to other areas as well, with people reporting suspicious packages from coast to coast.

A federal criminal investigation was launched to find the source of the anthrax at NBC, and health officials scrambled to retest the powder to see if it contained the bacteria. Initial tests had been negative, but authorities said the sample was so small they were reluctant to interpret the results.

During his broadcast Friday, Brokaw thanked viewers for their concerns and spoke highly of the 38-year-old O'Connor.

"She has been — as she always is — a rock. She's been an inspiration to us all," he said. "But this is so unfair and so outrageous and so maddening, it's beyond my ability to express it in socially acceptable terms. So we'll just reserve our thoughts and our prayers for our friend and her family."

Brokaw, who has appeared on NBC's evening newscasts for the last 18 years, later said in an interview on Dateline NBC that he would protectively take the anthrax antibiotic Cipro and believed most of his staff would too.

"The chances of anyone else contracting this are very low," he said. "But this is the ultimate nightmare. We just have to stay focused on what we know and not what we don't know."

NBC employees were evacuated from part of the 70-story GE Building in Rockefeller Center, which is home to Saturday Night Live, Late Night with Conan O'Brien and Brokaw's Nightly News.

About 10 blocks away in Times Square, employees on the third floor of The New York Times building were sent to other floors Friday after Judith Miller, a reporter who co-wrote a recent best seller on bioterrorism, opened a letter containing a powdery substance. A spokeswoman said the substance smelled like talcum powder.

The newspaper quoted Miller as saying the letter "contained future threats against the United States."

Executive Editor Howell Raines said initial tests showed that the powder did not pose any immediate problem. Air tests for radioactive and chemical substances were negative.

Mayor Rudolph Giuliani said officials were investigating five or six other reports of suspicious letters or powder Friday, but he said none appeared to be "of great concern."

"So far what we're dealing with is one case. The person is either fully recovered or on their way to full recovery," the mayor said. "That should give people some sense of comfort. ... This is treatable, and there are other antibiotics that can be used, and it is not contagious."

U.S. officials have told concerned residents that they should go about their normal business and not be alarmed by anthrax. They have also played down a link to terrorism, but Vice President Dick Cheney expressed skepticism Friday there was no relation. "I think the only responsible thing for us to do is proceed on the basis that it could be linked," he told PBS' NewsHour With Jim Lehrer.

News organizations across the country tightened mailroom security. The Associated Press, across the street from NBC, temporarily closed its mailroom, as did CBS. ABC stopped internal mail delivery in New York and Washington to allow a security evaluation, while CNN said it closed mailrooms in New York, Washington and Atlanta.

The Los Angeles Times building was quarantined for more than two hours Friday after employees found a "powder-like substance" on the floor; the substance was found to be harmless.

The anthrax scare began last week when a photo editor for The Sun supermarket tabloid in Boca Raton, Fla., died of the inhaled form of anthrax. The American Media building where Bob Stevens, 63, worked was sealed off after anthrax was found on his keyboard.

Two other employees turned out to have anthrax in their nasal passages, but neither has developed the disease. Both are taking antibiotics, and one has returned to work. No new infections have been found.

The Associated Press contributed to this report.