I'm not sure how, and I don't use Endpoint Protection.
However, it usually modifies your Internet Explorer Connection settings to use a Proxy of 127.0.0.1 or something. If you go into Internet Options, Connections, Lan Settings. Make sure there isn't anything under Proxy Settings that shouldn't be there. If it's like 127.0.0.1, uncheck it.
Also, it probably modified your hosts file. In WinXP that is under C:\Windows\System32\Drivers\ETC\hosts. You can open this file up in Notepad, but it might be marked readonly.
If you see anything out of the ordinary (Besides 127.0.0.1 localhost) you can use a # at the beginning of the line to remark it out. Might need to reboot for that to take effect.
That will keep you from using the redirect proxy temporarily, you'll likely have to check your PC with Malwarebytes or some other Malware/Spyware removal tool you are familiar with to clean up. (Again, I only say that because I'm not familiar with Endpoint Protection)