We’ve had threads on it before. A quick search reveals:
http://boards.straightdope.com/sdmb/showthread.php?t=636875&highlight=vigilink
http://boards.straightdope.com/sdmb/showthread.php?t=608769&highlight=vigilink
http://boards.straightdope.com/sdmb/showthread.php?t=614950&highlight=vigilink
Viglink isn’t malware. As Ed Zotti explains it,
Vendors pay Viglink a commission if anybody buys something after clicking on a link on the SDMB, and Viglink pays the SDMB a portion of that commission.