Infected masks were Kanohi masks tainted by Makuta's darkness. They were created when Kraata made physical contact with a mask. They could also be infected at long range by a shadow Kraata. An infected mask took on a rusted, pitted appearance. Anyone wearing such a mask became subservient to the will of Makuta.2
Notes
Infected Kanohi masks were tainted by the evil power of Makuta. They appeared scarred, rusted, and pitted. Anyone who donned an infected mask became a servant of Makuta and would obey his will until the mask was removed.3
The Brotherhood of Makuta apparently made use of Rahi controlled by infected masks in their war with the Dark Hunters.4
The infection of a mask essentially formed a connection between the being wearing it and a Makuta. The Makuta did not need to actively focus on each and every being wearing one of his infected masks to control them. A Makuta could not infect another Makuta's mask.5
It took a great deal of power used by more than one Toa to cleanse an infected mask. Because of the enormous amount of energy required, the Toa did not do this often.6, 7 The Toa used the same ritual they used to heal Tahu Nuva, but it required all six Toa to do it.8, 9
If an infected mask and a krana were placed on the same Rahi, the influence of the infected mask would win out, since Makuta's essence was much more powerful.10
The effect of antidermis and the effect of infected masks were similar in strength.11
Infected Kanohi likely didn't contain antidermis.12
Infected masks were rusty.13
The Masks of Light, Time, and Life could probably be infected.14
Powerless masks could be infected.15
Infected masks could be cleansed.16
All six Toa needed to work together to cleanse an infected mask.17