The biggest threat

Barclay returned to his work station after talking to the captain. Now that he had confirmed it would work he estimate three weeks before the entire crew was completly under.

That is everyone except one particular member, one being that wouldn't be effected by the holodeck. Data.

The mind control device was ment to work on organic brains, not other computers. When the ailens had taken over the ship it had been Data that had broken their control, and Barclay had no doubt that the android would be able to undue his plans.

Having one of Data's friends get close enough to turn him off was always an option, but it would be Barclay's last option. He would need Data's smarts to impliment stage two of his plan.