A "disease vector" is a Web site or URL known to distribute Internet threats including spyware, password-cracking applications, key-stroke trackers, virus kit downloads, and other security threats.
Another category of disease vectors are sites made to look legitimate, but below the surface the hacker directs all the "back-end" functionality -- links, data posts, etc. to his or her own locations.
Trend Micro quickly adds confirmed malicious sites to the phish and spyware pattern file so you can prevent LAN clients from downloading the security threats, or from being duped by the look-alike sites.