Mark Boslough tends to keep a low profile each year on this particular day. As the proliferator of more than a couple of famous e-mail hoaxes, the Sandia National Laboratories physicist knows he's a prime target for April Fools' Day pranksters.

So on this of all holidays, he likes to keep his skepticism at the ready.

"We're all subject to gullibility, especially if it's something you want to believe," Boslough said. "That's why con artists continue to be successful."

Getting one past Boslough might be tough, though — his most well-known prank is ranked seventh out of the "Top 100 April Fool's Day Hoaxes of All Time," at the Museum of Hoaxes, museumofhoaxes.com.

Boslough just couldn't help himself with that one, which he let loose on cyberspace back in 1998 — he said he just had to spread the word about Alabama legislators trying to change pi, an infinite number that begins with 3.14159, to the more "biblical value" of 3.0.

The e-mail was disguised as a news story, written by "April Holiday" of "The Associalized Press."

In it, a fictitious lawmaker argued that because pi can't be calculated exactly, it could "harm students' self-esteem."

The story actually started as a small prank between Boslough and some friends at New Mexicans for Science and Reason, a scientific group that often debunks urban myths and pseudoscientific propaganda.

But Boslough soon found his attempt to poke fun at creationists, a group that wants religious ideas discussed in school science classes, had gone viral, he said.

"I was just curious," Boslough said. "I always wondered if I wrote something like that if people would forward it."

When Boslough e-mailed him the story, Dave Thomas, a seismologist and president of NMSR, posted it on a usenet group called talk.origins — on online bulletin board where both creationists and scientists would often debate their ideas, Thomas said.

"On the morning of April 1, I posted it as pretty much a straight news story," Thomas said. "Then about 12 hours later, I posted that it was a prank, but by then it had already spread."

Soon, calls poured into Alabama legislators' offices to protest the new law. And the e-mail started to change — with versions coming back to Boslough and Thomas attributing the story to the Associated Press and changing fictitious source names into those of real people at Auburn University, Thomas said.

"It was like looking at a virus as it mutates," Thomas said.

Eventually the story was debunked by Snopes.com, a site that dispels urban myths; it was also cited by National Geographic News in 2004 as one of the "more memorable hoaxes in recent history."

The prank faced stiff competition at the Museum of Hoaxes for the No. 1 spot. It was beaten by a story in 1957 about "The Swiss Spaghetti Harvest" and a 1996 one about "The Taco Liberty Bell," among others, but Boslough said he was amazed by how far his joke ascended.

"Being in the top 10 is an honor beyond my imagination when I wrote that thing," Boslough said with a laugh.

And his pranks certainly didn't stop with that one.

Emboldened by his success with the pi story, Boslough struck again in 1999, with a fake Darwin Award about an Alaska worker who was cooked and killed in microwave radiation after standing too close to a telecommunications feed horn.

It said the worker, "Edward Baker," was killed while trying to keep warm. Other sources in the story included "Tanya Cooke" and "John Burns," which were subtle hints that it was a joke, Boslough said.

"I got one of those Darwin Award e-mail forwards and I basically wrote my own award, cut it and pasted it at the top as the winner," Boslough said. "Amazingly enough, I was at my mom's house up in Denver not long after, and it was on the front page in the Denver Post in somebody's column — the award I made up."

That prank had the worker employed with the Northern Manitoba Signal Relay Company, which doesn't exist. Boslough used the name so he could abbreviate it to NMSR, in hopes that Thomas would pick it up, he said.

"I knew Dave always checked that acronym online every day, so I was hoping he'd find it," Boslough said.

Thomas said he did indeed notice the story, and he was suspicious from the beginning.

"I think Mark did that one for my benefit, but he didn't get me," Thomas said.

Thomas also launched his own April Fools' Day prank that year, with a little help from Boslough. His prank didn't go quite as viral as Boslough's, but it still managed to fool quite a few people — especially in creationist camps, he said.

Thomas' prank was an e-mail sent out by a fictitious German graduate student named "Stefan" who claimed that scientists in New Mexico were covering up a fossil find that showed a dinosaur eating a species of early man.

"Stefan" felt compelled to spread the word that the find had disproved Darwin's theory of evolution, because the theory shows dinosaurs and hominids could not have existed at the same time.

And Thomas' prank even came with pictures.

"My dad had some fossils, so we arranged it to make it look like a dinosaur eating a human," Thomas said. "The story spread to several creationist Web sites, with them using it as proof of their ideas."

The original story and photos, which include Thomas playing the role of a paleontologist, remain on NMSR's Web site at www.nmsr.org/Archive.html — and he still gets an occasional call from a creationist asking for more details about the find, Thomas said.

"We tell them to go up a level on the site and check where they are," he said.

When asked if they had any mischief planned for today, the two scientists said, perhaps a bit too innocently, that they didn't.

But Boslough did pass on a few tips for would-be pranksters and skeptics.

"I do have some rules for hoaxes," Boslough said. "Don't be mean, don't humiliate people — you want them to laugh. Remember that the best jokes have lots of clues in them, and also, on the Internet, you want about half the people to get the joke and half to not get it."

Contact Sue Vorenberg at svorenberg@sfnewmexican.com.