There are several different types of Bitcoin clients. Hybrid server-assisted clients like Electrum get a lot of their network information from centralized servers, but they also check the server's results using blockchain header data. This is perhaps somewhat more secure than either server-assisted clients or header-only clients. ertised sites are not endorsed by the Bitcoin Forum. They may be unsafe, untrustworthy, or illegal in your jurisdiction. Advertised sites are not endorsed by the Bitcoin Forum. They may be unsafe, untrustworthy, or illegal in your jurisdiction. Advertise here.