The remote FreeBSD host is missing a security-related update.
The Piwik security advisory reports : The Piwik 1.5 release addresses a critical security vulnerability, which affect all Piwik users that have let granted some access to the 'anonymous' user. Piwik contains a remotely exploitable vulnerability that could allow a remote attacker to execute arbitrary code. Only installations that have granted untrusted view access to their stats (ie. grant 'view' access to a website to anonymous) are at risk.