The only reference I've been able to find is in the DS9 novel : Lesser Evil
"“You resisted the assimilation,” Bowers said. “How?”
A third arm grew out of the center of the Founder’s narrow chest and
opened its slender, symmetrical, two-thumbed hand. The arm lengthened
until the hand was only inches away from Bowers’s face. In the center
of its palm, Vaughn saw, was what looked like a black pebble.
“The nanoprobes?” Bowers guessed.
“They were trying to overwhelm me,” she said. “They were quite
painful. They kept twisting me inside out. I knew I had to make them
stop. So I did the only thing I could think of. I squeezed them
together until they stopped.”
“Mr. ch’Thane,” Vaughn said. “Explain, please.”
Shar shook his head. “She’s fine. She really was able to withstand the
“How?” Bowers asked.
Shar continued studying his tricorder. “Borg nanoprobes are designed
to assimilate life-forms on a cellular level. But a changeling’s
morphogenic matrix has no cellular structure in its natural state. In
essence, it was as if the nanoprobes were trying to assimilate a body