Which of the following is prohibited?

The FCC strictly prohibits any willful or malicious interference with radio communications. This rule is a cornerstone of the Amateur Radio Service, ensuring that the limited RF spectrum remains usable and fair for all operators. Deliberately jamming or disrupting another station's transmission is a serious violation of Part 97 rules. The other options listed are completely legal. International communications on VHF/UHF bands can happen via satellites, Earth-Moon-Earth (moonbounce), or tropospheric ducting. Third-party traffic using digital modes is also perfectly acceptable, provided the communication complies with standard third-party rules.