We provide a collection of minor results on the area of Instant Messaging (IM) worms, which has received relatively little attention in the formal literature. We review selected IM worms and summarize their main characteristics, motivating a brief overview of the network formed by IM contact lists, and a discussion of theoretical consequences of worms in such networks. Existing methods to restrict an IM worm epidemic are analyzed in terms of usability and e#ectiveness, leading to the suggestion of two minor variations to limit IM worm propagation. We believe these variations are more user-friendly and e#ective than existing published methods. We also provide brief results of a three and a half year user study of IM text messaging and file transfer frequency in a moderate-size public IM network -- the largest such study to date -- which is of independent interest, but also supports in part the preceding claim regarding user-friendliness.

Most cryptographic algorithms provide means for secret and authentic communication. However, for many situations and individuals the ability to repudiate messages or deny a conversation is no less important than secrecy. Whistleblowers, informants, political dissidents and journalists, to name a few, are all people for whom it is of utmost importance to have means for deniable conversation. For those users electronic communication must mimic face-to-face private meetings. Off-the-Record Messaging, proposed in 2004 by Borisov, Goldberg and Brewer, and its subsequent improvements, simulate private two-party meetings. Despite some attempts, the multi-party scenario remains unresolved. In this work we tackle the issue of multi-party off-therecord instant messaging. Our first goal is to identify the properties of multi-party private meetings. Differences not only between the physical and electronic medium but also between two- and multi-party scenarios are important for the design of private chatrooms. Our proposed solution takes into account these differences and is suitable for composition with extensions having other privacy preserving goals, such as anonymity. 1