200px-XANA's Nanites

In the episode "Amnesia," X.A.N.A. created a Nanobot and injected it into Mrs. Hertz's collection of nanobots. Later, as a prank, Odd put the nanobot unknowingly on Ulrich's nose, where it crawled into his nasal passages and into his brain, where it wiped out his memory centers, giving him amnesia. When Sissi came to visit Ulrich in the Infirmary after he fainted, the nanobot spread to her body, then to Herb's, Nicholas's, and eventually to the rest of the school's, giving them all memory loss. Once the Tower, X.A.N.A. had activated, was deactviated, Jeremie activated a time reversion. This time, Ulrich burnt the nanobot substance to end the threat.