Issue addressing is a vital task in the evolution of software projects. However, in practice, not all issues can be addressed on time. To facilitate the issue addressing process, monetary incentives (e.g., bounties) are used to attract developers to address issues. There are two types of core roles who are involved in this process: bounty backers, who propose bounties for an issue report via bounty platforms (e.g., Bountysource), and bounty hunters, who address the bounty issues and win the bounties. We wish to study the process of bounty issue addressing from the angle of two important roles (i.e., backers and hunters) and their related behaviors. With a better understanding of how they address bounty issues, stakeholders (e.g., operators and developers) of open source projects may have a reasonable estimation of what they can expect from backers and hunters. In this study, we investigate 2,955 bounty backers and 882 bounty hunters, and their associated 3,579 GitHub issue reports with 5,589 bounties that were proposed on Bountysource. We find that: 1) Overall, the value of a bounty is small (median bounty value of $20). Both individual and corporate backers prefer to support implementing new features rather than fixing bugs. Corporate backers tend to propose larger bounties and propose bounties more frequently than individual backers. 2) 85.0% of the bounty hunters addressed less than 3 bounty issues. The income of 56.7% of the bounty hunters is no more than $100 and only 2.7% of the hunters have earned more than $2,000. In addition, most of the regular hunters and big hunters are developers that made at least one commit before addressing a bounty issue. 3) The value of a bounty issue is not a statistically significant factor that attracts developers that have never made any commit before to address an issue. Based on our findings, we provide several suggestions for stakeholders of open source projects and hunters.