Definition
The Digital Millennium Copyright Act is a U.S. law passed in 1998 that, among other provisions, established a notice-and-takedown system for online copyright infringement. Copyright holders can send a DMCA notice to an online service provider identifying allegedly infringing content; the provider gains liability protection (a 'safe harbour') if they remove the content promptly. The mechanism applies to web hosts, social media platforms, ISPs — and VPN providers.
DMCA and VPNs
When a copyright enforcement firm observes a BitTorrent swarm, they log the IPs of every participant and send DMCA notices to the operators of those IPs. If the IP belongs to a VPN provider, the notice arrives at the provider rather than the user. A provider with logs can identify the subscriber and may forward the notice or take action against the account; a no-logs provider has no record to act on. This is one of the operational reasons no-logs policies matter beyond ideology.
Provider Responses
Providers handle DMCA notices very differently. Some block BitTorrent on US-based servers entirely to avoid the headache. Some have public policies of ignoring notices on the grounds that they cannot identify users. Some are based outside U.S. jurisdiction and reply that DMCA does not apply to them. The provider's stance is a useful signal of their broader privacy posture.