In response to feedback from operational security communities, CAIDA's source address validation measurement project (https://spoofer.caida.org) is automatically generating monthly reports of ASes originating prefixes in BGP for systems from which we received packets with a spoofed source address. We are publishing these reports to network and security operations lists in order to ensure this information reaches operational contacts in these ASes. This report summarises tests conducted within usa, can. Inferred improvements during May 2021: ASN Name Fixed-By 5078 ONENET-AS-1 2021-05-19 55016 IMPER-AS-1 2021-05-25 Further information for the inferred remediation is available at: https://spoofer.caida.org/remedy.php Source Address Validation issues inferred during May 2021: ASN Name First-Spoofed Last-Spoofed 3356 LEVEL3 2016-03-06 2021-05-05 209 CENTURYLINK-US-LEGACY-QWEST 2016-08-16 2021-05-25 20412 CLARITY-TELECOM 2016-09-30 2021-05-31 6181 FUSE-NET 2016-10-10 2021-05-29 11427 TWC-11427-TEXAS 2016-10-21 2021-05-28 174 COGENT-174 2016-10-21 2021-05-11 30036 MEDIACOM-ENTERPRISE-BUSINESS 2016-11-16 2021-05-25 22898 ATLINK 2016-12-16 2021-05-28 63296 AWBROADBAND 2017-09-01 2021-05-27 546 PARSONS-PGS-1 2017-11-20 2021-05-20 393564 SPOKANE 2018-06-05 2021-05-18 33452 RW 2018-09-19 2021-05-26 20448 VPNTRANET-LLC 2018-09-20 2021-05-28 5078 ONENET-AS-1 2020-04-06 2021-05-24 6391 URBAN-15 2020-05-29 2021-05-20 208188 PUGET-SOUND-NETWORKS 2020-12-04 2021-05-30 62684 XLBROADBAND 2021-05-19 2021-05-19 13876 FIBER-64 2021-05-20 2021-05-27 26397 OPTIPUTER 2021-05-24 2021-05-24 3754 NYSERNET3 2021-05-24 2021-05-24 3756 NYSERNET3 2021-05-24 2021-05-26 20150 ANYNODE 2021-05-29 2021-05-29 Further information for these tests where we received spoofed packets is available at: https://spoofer.caida.org/recent_tests.php?country_include=usa,can&no_block=1 Please send any feedback or suggestions to spoofer-info@caida.org