Norwalk-based Splinternet Holdings Inc. this week acquired privately held Vidiation Inc. of Illinois, a development-stage radiation detection marketing company, in a stock deal.

Splinternet's main product is the DefenTect radiation detection and alert system that is designed to find "dirty bombs."

Dirty bombs combine a conventional explosive such as dynamite with radioactive material.

Publicly traded Splinternet issued about 4.8 million common shares of Splinternet stock to former Vidiation shareholders, who now own 7.8 percent of the Norwalk company.

Yesterday, Splinternet shares closed at $1.52, down 3 cents. The stock trades over the counter on the Nasdaq Bulletin Boards under the symbol SLNH.

Laura Wessner, Splinternet's vice president of corporate development, said Vidiation's name will change at a later date, and it will remain in Illinois and other locations. Splinternet and Vidiation each employ six people and Splinternet might hire a few more, she said.

Vidiation was formed in 2006 to market advanced homeland security technologies as a defense against the worldwide threat of terrorism. Previously, Vidiation and Splinternet had cross-reseller agreements for radiation detection technologies.

Wessner said Splinternet acquired Vidiation for its marketing experience.

"Vidiation and Splinternet are dedicated to developing integrated protection systems to thwart illegal transport of radiological source material," said James Ackerly, chief executive officer of Splinternet. "By working together, next-generation radiological detection systems will be accelerated to market."

Splinternet plans to announce customers for DefenTect after contracts are signed, Wessner said.

A large market exists for Splinternet products, said William Vassel, chairman and chief executive officer of Stamford-based Murdoch Security Group, which provides security guards for events and individuals.

"Our biggest security threat is probably from a dirty bomb," Vassel said. "Former four-star generals have told me that if we are going to be hit, it will likely be with a dirty bomb, most likely in a large metropolitan area like New York City. "There should be a demand going forward (for Splinternet products) because the evildoers have not gone away."