Sharing security events is deemed of critical importance to counteract large-scale network-based attacks (e.g., DDoS, DrDoS) at Internet service provider (ISP) networks as these attacks have become larger, more sophisticated and frequent. On the one hand, security event sharing is regarded to speed up organization's mitigation and response capabilities. On the other hand, it is currently done on an ad-hoc basis via email, member calls or in personal meetings only under the premise that participating partners are personally known to each other. As a consequence, mitigation and response actions are delayed and thus security events are not processed in time. One approach to reduce this delay and the time for manual processing is to disseminate security events among trusted partners. To facilitate the exchange of security events in conjunction with widely adopted monitoring technologies, in particular network flows, we make use of the exchange format FLEX. To overcome delayed response actions and manual processing of security events, we present a communication process that supports the dissemination of threat information based on FLEX in context of ISPs. We show that this communication process helps organizations to speed up their mitigation and response capabilities without the need to modify the current network infrastructure, and hence make it viable to use for network operators.