Cyberweapons raise new problems in ethics. We first discuss the peculiarities of cyberweapons in the array of modern weapons. We then discuss five areas of ethical issues that are primarily unique to cyberweapons: attribution, product tampering, unreliability, damage repair, and collateral damage, with special attention to the latter. Although cyberweapons are generally nonlethal, they can hurt large numbers of civilians; we estimate that the collateral damage of the Stuxnet attacks on Iran in U.S. dollars was $2.9 million, similar in cost to that of a human death. Cyberattacks raise additional ethical issues in their need to impersonate civilians, what can be called cyber perfidy; in the difficulty of tracking their damage; and in the problem of accurately measuring the damage of an often widely-distributed attack. We conclude that many of the ethical issues of cyberweapons are intractable, and international agreements should be sought to control them.