IWSVA found that the requested URL belongs to one of the URL Filtering Categories, and the requesting user is a member of a policy that disallows that type of content

IWSVA triggered a match with a user-specified Block List rule

A Block List rule (HTTP > URL Access Control > URL Blocking | Via Local List) contains a wildcard that triggers unexpected matches

The URL contains a string (portion or entire) which matches a keyword specified in the Local List Match (HTTP > URL Access Control > URL Blocking | Via Local List).

The URL, domain, or keyword was specified in an imported Block list that is not immediately visible from the IWSVA console

A recent virus or filtering event occurred at the same URL (IWSVA will block all subsequent requests to the site for a period of four hours)

URL is a known spyware site

False positive in the Web Reputation database (report to Trend Labs)

Incorrect/inappropriate content in an Imported block list used by URL Blocking or URL Filtering

There is an error in a pattern file (rollback to last known "good" file)