By default your antivirus software may disable writing to the hosts file.
Most virus protection software will allow you to change this default setting.
Your antivirus may also may restrict writing to certain files. You may encounter an error such as
[ERROR] Cannot open Windows EventLog; check privileges, or start server with --log_syslog=0
in you mysql log file. In this case, your antivirus is restricting write access to files with .log extensions.