Nowdays, I noticed that many times malware attacks hosts file. They modify it and redirect antivirus sites to their IPs. To avoid this we need to lock file. Zone alarm has option to lock hosts file. But if u want it without any tool just do it as below.
Go to CMD prompt in windows by start –> run –> cmd
type following commands
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cd c:windowssystem32drivers
attrib +R hosts
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this will lock host file in windows xp
