According to international law, anonymity of the voter is a fundamental precondition for democratic elections. In electronic voting, several aspects of voter anonymity have been identified. In this paper, we re-examine anonymity with respect to voting, and generalise existing notions of anonymity in e-voting. First, we identify and categorise the types of attack that can be a threat to anonymity of the voter, including different types of vote buying and coercion. This analysis leads to a categorisation of anonymity in voting in terms of a) the strength of the anonymity achieved and b) the extent of interaction between voter and attacker. Some of the combinations, including weak and strong receipt-freeness, are formalised in epistemic logic.