A false positive in McAfee's security has spooked some, following an update this week. The suite would identify JavaScript files that were benign in nature as being viruses, preventing access to them. Primarily, certain websites were affected, though the extent of the "damage" pretty much ends there.
McAfee pulled the update after the flaw was discovered on Wednesday and has already issued a fix. Several false positives have been present in high-profile security suites the past year, such as Symantec accidentally crippling certain versions of Windows. That is the inherent risk these companies take in needing to supply updates so fast, so these sorts of issues are expected from time to time.