CaSIs is short for Common and Stubborn Infectors. These are malicious programs (Viruses, Worms, Trojans, etc.) that are notoriously difficult to detect and to remove by regular anti-virus programs. These malicious programs often have the capability to disable your computer or your anti-virus programs.
Good examples of these infectors are:
Trojan.Win32.Small.wv (Medichi &...