So I installed avast earlier today. Went through the setup process, it asked if I wanted to install anti-theft, I said yes, it installed and then said I needed to reboot my phone. It also asked for superuser permission, which I granted.
But my phone went into a constant reboot cycle. After booting into the home screen, it rebooted by itself after a short while.
In the short time window before it reboots, I managed to uninstall avast mobile security, and the rebooting stopped. But the anti-theft is still there (under the fake name). I never set it up because as soon as I installed it the rebooting started.
So what should I do? I can’t uninstall anti-theft… I can find it in the phone’s application list (under the fake name), but there’s only the option to force close, not uninstall
hi i can not help you as long as i do not see any logs on the bootup process (until restart) 
Have you tried a soft reset (pull the battery out, wait a minute, then reinstall the battery and restart the phone) to see if this stops the constant reboot?
Have you tried a hard reset (last option for a fix)? This will wipe out ALL data on your phone and put it to factory settings, and hopefully you have a backup.
I recommend that when you install any app. that you reboot your phone at that time prior to opening it and playing around with settings, just like you would do with a PC, but this is just my opinion.
It is also recommended, as you already know, to uninstall Anti-Theft prior to uninstalling Avast Mobile Security. Do you have a task manager on the phone where you can find this fake name to uninstall the Anti-Theft? Otherwise, the hard reset might be your only option unless one of the Moderators has another suggestion.
Is it SGS with Gingerbread? Could you please tell me the baseband and kernel version? Thx.