  With an ever-increasing amount of open source software, the popularity of
services like GitHub that facilitate code reuse, and common misconceptions
about the licensing of open source software, the problem of license violations
in the code is getting more and more prominent. In this study, we compile an
extensive corpus of popular Java projects from GitHub, search it for code
clones and perform an original analysis of possible code borrowing and license
violations on the level of code fragments. We chose Java as a language because
of its popularity in industry, where the plagiarism problem is especially
relevant because of possible legal action. We analyze and discuss distribution
of 94 different discovered and manually evaluated licenses in files and
projects, differences in the licensing of files, distribution of potential code
borrowing between licenses, various types of possible license violations, most
violated licenses, etc. Studying possible license violations in specific blocks
of code, we have discovered that 29.6% of them might be involved in potential
code borrowing and 9.4% of them could potentially violate original licenses.
