Symantec LiveUpdate before 1.6 does not use cryptography to ensure the integrity of download files, which allows remote attackers to execute arbitrary code via DNS spoofing of the update.symantec.com site.
Symantec LiveUpdate 1.4 through 1.6, and possibly later versions, allows remote attackers to cause a denial of service (flood) via DNS spoofing of the update.symantec.com site.