Use Avast to clean it up....then
take it offline. Otherwise you're just using band-aids to combat cancer. You might also run Spybot Search and Destroy version 1.6 if you can find it. Just be sure to turn off Avast temporarily so you don't risk "false-positives" showing up in either program. Using Spybot- not run in resident memory to counter a potential existence of other malware Avast might not pick up.
Microsoft won't support a required security level of this product. Don't expect Avast- or Spybot to make up the difference.
I once gave this all much thought. Even considered running a third-party firewall like Comodo. But I read far too much about how inherently vulnerable XP became as an officially unsupported operating system. Just too many ways for hackers to get deep inside the OS itself. Where antivirus and malware programs may function as mere "idiot lights", only telling you about intrusions after the fact.
Unfortunately from a business perspective, when an OS developer no longer supports an earlier version, it's generally not cost-effective for third-party developers to pick up where they left off. So eventually you end up seeing many of them simply abandon support as well. Worse if they choose to do so in part rather than in whole. It's just too risky to run XP online now.
But offline, think of all those old programs and games you can still run. And without any anti-virus/security programs that take up so much resident memory. Equally you can turn off any number of XP services not required while running offline, so you can reclaim a great deal of memory for your primary apps and games.
I think of my legacy system as my own Tardis. A way of going back in time about 15 years.
Windows XP services that can be safely DISABLED! - Forums