**5. Conclusions**

This paper presents an LS-PSO algorithm for solving the IPTBK problem. The proposed algorithm can analyse the effects of multiple-swarm search strategies on the quality of PSO solutions to improve the reconstruction accuracy for the probable paths of DDoS attacks. The experimental results confirmed that the proposed algorithm can analyse the possible attack paths of botnets and the attack sources of DDoS threats by IP traceback techniques with the LS-PSO algorithm.

Although the proposed algorithm can solve the IPTBK problem, its use entails practical challenges. For example, in the case of a DDoS attack, the proposed algorithm generates unusually high rates of packet loss across a network, which may disorder the sequence of packet marking and thus may reduce the traceback accuracy of the algorithm. To implement rapid countermeasures against cyber-attacks involving DDoS flooding in highspeed networks, such as 5G networks, partial packets with high rates of packet loss must be collected. A future study will examine the minimum number of packets required to determine the origins of attacks.

**Author Contributions:** Conceptualization, P.W.; methodology H.-C.L. and K.-M.C.; resources, P.W.; formal analysis, H.-C.L.; data curation, H.-C.L.; writing—original draft, H.-C.L. and W.-H.L.; writing— review and editing, P.W. and K.-M.C.; software, H.-C.L. and Z.-Y.Y.; validation, H.-C.L. and W.-H.L.; visualization, H.-C.L. and Z.-Y.Y.; project administration, P.W.; funding acquisition, P.W. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Ministry of Science and Technology of Taiwan under gran<sup>t</sup> no. MOST 108-3116-F-168-001-CC2, no. MOST 109-2410–H-168-005 and the green energy technology research center on the featured areas research center program within the framework of the higher education sprout project from Ministry of Education (MOE) of Taiwan.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available upon request from the corresponding author.

**Conflicts of Interest:** The authors declare no conflict of interest.
