I'm using Malwarebytes as well, but unfortunately the version I'm using wont' update anymore, but still good to keep around...
If you like MBAM, it still works and updates on XP.
"...Malwarebytes support for legacy Windows XP and Vista Operating Systems Malwarebytes 3.5, will continue to support legacy Windows XP and Windows Vista at the same level as we had with earlier 3.x releases. In order for Malwarebytes to better support these legacy operating systems we’ve designed Malwarebytes 3.5 with special compatibility features to allow on-going protection updates and other maintenance upgrades via a separate development track..."
Some long reading on details:
https://forums.malwarebytes.com/topic/286840-mbam-221-no-definitions-updates-after-may-19/page/4/
The skinny:
I had/have the free version. I don't think I used or needed the clean tool, (can't remember) I think it's for uninstalling paid versions(?) but if you use a licensed version make sure you have your lic# before cleaning!
mbam-clean-2.3.0.1001.exe
downloads.malwarebytes.org/file/mbam_clean
I installed: mb3-setup-legacywos-3.5.1.2522-1.0.365-1.0.5292.exe
https://downloads.malwarebytes.com/file/mb3_legacy
The slight down side is it also installs as a service which loads on automatic. I changed it to disabled and only start it when I run a scan.
I used it on two 'puters yesterday; checked the downloads just now, working.