Immubots are Nanobots which live in the bloodstream and act to protect the host from disease and monitor their health internally. Their programming can be updated by a doctor via accessing the wristpatch.
Like most bots, immubots come in different variations from different sources. Some are high alert, ready for anything out of the box, and others are just based on GC standard medical protocol (keeps known viruses and diseases at bay, not species specific enough to cater for the needs of the Sianat, for example).
Others are bought illegally, without a GC "licence" of sorts and as a result can be badly programmed, not pass Shuttleport checks and other scanners. It is implied these can be fixed but having non GC approved immubots is regarded by most major characters as something defenitely not positive and also quite risky.