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I have noticed for some time that the shared screen icon flickers on and off on my menubar every couple of minutes (MacBook Pro, MAC OS X 10.8.4). I thought it was a glitch or a bug. I've checked the console and there are connection attempts almost every minute. 99% are from a specific address:

26/07/13 00:41:51,569 screensharingd[49866]: Authentication: FAILED :: User Name: N/A :: Viewer Address: :: Type: VNC DES

Is this a brute force attack? Should I be concerned? I do need Screen Sharing on, as I connect to this mac quite frequently. I considered activating the Firewall, but it won't help unless I block all incoming connections.

Is there a way to block that IP from connecting at all. The mac is behind an airport extreme router with VNC ports pointed to this mac by NAT. Any way to filter those connections at that level?

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You could probably use IceFloor to configure the mac firewall to block connections from that one IP address. –  Jozef Legény Jul 26 '13 at 8:34
You might be better off denying access to the VNC ports to all IP addresses except the places you wish to have remote access. –  Bert Jul 3 at 14:22

1 Answer 1

IP Blacklisting isn't a very effective means of defence. IPs are so abundant, most people are on dynamic IPs, so if they find themselves being blacklisted, they just need to restart their modems and be assigned a different IP form their ISP. I recommend trying to change your own IP, and use strong passwords.

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