  Interest in unethical user interfaces has grown in HCI over recent years,
with researchers identifying malicious design strategies referred to as ''dark
patterns''. While such strategies have been described in numerous domains, we
lack a thorough understanding of how they operate in social networking services
(SNSs). Pivoting towards regulations against such practices, we address this
gap by offering novel insights into the types of dark patterns deployed in SNSs
and people's ability to recognise them across four widely used mobile SNS
applications. Following a cognitive walkthrough, experts (N=6) could identify
instances of dark patterns in all four SNSs, including co-occurrences. Based on
the results, we designed a novel rating procedure for evaluating the malice of
interfaces. Our evaluation shows that regular users (N=193) could differentiate
between interfaces featuring dark patterns and those without. Such rating
procedures could support policymakers' current moves to regulate deceptive and
manipulative designs in online interfaces.
