INSIDE the depths of the Plum Island Animal Disease Center, past the security guards and locked gates, new waterproof cameras watch the hallways and the cows, pigs and scientists passing through.

Eight months have passed since the Department of Homeland Security took over the management of Plum Island from the Agriculture Department, and last week, Homeland Security officials offered a rare glimpse into this veiled and mysterious island less than two miles off the North Fork. The timing of the tour for a dozen journalists coincided with the publication of a new book, ''Lab 257,'' by Michael Christopher Carroll, who argues that the Plum Island laboratories have an appalling safety record and can be linked to outbreaks of Lyme disease and West Nile virus.

But Homeland Security officials dismissed the book's claims and said during the daylong tour that they had bolstered security on the 840-acre island. ''The Department of Homeland Security takes security tremendously seriously,'' said Maureen McCarthy, the department's director of research and development. ''This is our business. This is our job. This is what we're supposed to do.''

There have long been questions about the safety of Plum Island's operations, but they became more prevalent after the Sept. 11 terrorist attacks. Mr. Carroll, a lawyer from Bellmore, writes that in 2002 American forces in Afghanistan found a file on the Plum Island laboratory in the home of a nuclear physicist identified by American officials as an associate of Osama bin Laden.