X parasite 

A breed of organic life, the X Parasites are the most dangerous species of sentient life in the universe. They can infest themselves in a host body, thereby creating them a new body to live in.

"X Parasites are dangerous, man."

X parasite by FinalHazard April 25, 2004

X parasite 

A parasitic life-form that obtains a new host body by destroying the original and creating a copy.
An X Parasite samples DNA data from previous hosts and can then change it's shape accordingly. X Parasites have been known to copy the actions of the hosts so perfectly that often there are X Parasites walking in the streets of you local city and nobody even realises it.
The X Parasite, if threatened, will destroy a life-form and steal it's DNA.

Proceed with caution, it is expected that the X Parasites have infected the area.

X parasite by Mechacrazie2k August 12, 2005