Michalis Pachilakis

Emmanouil Karampinakis, Michalis Pachilakis, Panagiotis Papadopoulos et al.

Bitcoin is the first and undoubtedly most successful cryptocurrecny to date with a market capitalization of more than 100 billion dollars. Today, Bitcoin has more than 100,000 supporting merchants and more than 3 million active users. Besides the trust it enjoys among people, Bitcoin lacks of a basic feature a substitute currency must have: stability of value. Hence, although the use of Bitcoin as a mean of payment is relative low, yet the wild ups and downs of its value lure investors to use it as useful asset to yield a trading profit. In this study, we explore this exact nature of Bitcoin aiming to shed light in the newly emerged and rapid growing marketplace of cryptocurencies and compare the investmet landscape and patterns with the most popular traditional stock market of Dow Jones. Our results show that most of Bitcoin addresses are used in the correct fashion to preserve security and privacy of the transactions and that the 24/7 open market of Bitcoin is not affected by any political incidents of the offline world, in contrary with the traditional stock markets. Also, it seems that there are specific longitudes that lead the cryptocurrency in terms of bulk of transactions, but there is not the same correlation with the volume of the coins being transferred.

Michalis Pachilakis, Panagiotis Papadopoulos, Nikolaos Laoutaris et al.

The Real Time Bidding (RTB) protocol is by now more than a decade old. During this time, a handful of measurement papers have looked at bidding strategies, personal information flow, and cost of display advertising through RTB. In this paper, we present YourAdvalue, a privacy-preserving tool for displaying to end-users in a simple and intuitive manner their advertising value as seen through RTB. Using YourAdvalue, we measure desktop RTB prices in the wild, and compare them with desktop and mobile RTB prices reported by past work. We present how it estimates ad prices that are encrypted, and how it preserves user privacy while reporting results back to a data-server for analysis. We deployed our system, disseminated its browser extension, and collected data from 200 users, including 12000 ad impressions over 11 months. By analyzing this dataset, we show that desktop RTB prices have grown 4.6X over desktop RTB prices measured in 2013, and 3.8X over mobile RTB prices measured in 2015. We also study how user demographics associate with the intensity of RTB ecosystem tracking, leading to higher ad prices. We find that exchanging data between advertisers and/or data brokers through cookie-synchronization increases the median value of displayed ads by 19%. We also find that female and younger users are more targeted, suffering more tracking (via cookie synchronization) than male or elder users. As a result of this targeting in our dataset, the advertising value (i) of women is 2.4X higher than that of men, (ii) of 25-34 year-olds is 2.5X higher than that of 35-44 year-olds, (iii) is most expensive on weekends and early mornings.