450 Blocked by Windows Parental Controls
Meaning
A Microsoft extension code indicating that the request was blocked due to Windows Parental Controls being turned on.
When to Use
Used by Microsoft (for example, in Windows Live Family Safety) when content is blocked for a user due to parental control settings. The server or intermediary filters the request and returns this status to explain the block.
Example
When a child account attempts to access a site or resource disallowed by parental controls, the system may return 450 Blocked by Windows Parental Controls, indicating the content is blocked by policy.
When Not to Use
Do not use outside the context of Microsoft’s parental control systems. It's not a standard HTTP status. For general content filtering, a 403 Forbidden might be used with a custom message instead.
Source
Unofficial (Microsoft)