Firewalls are usually paired with intrusion prevention systems (IPSs), as well as with endpoint security systems (also called anti-X and gateway anti-malware systems). IPSs provide another layer of internal security by detecting and blocking known malicious traffic and anomalous traffic patterns. Endpoint security systems check remote client devices for viruses and ensure that client software is in compliance with the organization's current software versions and standards. They also support URL, or content filtering. In addition, most firewalls today inherently support virtual private network (VPN) technology, which encrypts data to avoid its theft in transit.