Litecoin is P2P (Peer-to-Peer) network and software client...
Due to the way that the Litecoin software works, you have no real choice over which other computers on the internet, that are also running Litcoin, that your PC will connect to! This could obviously be 'problematic' and unfortunately most firewalls don't protect you against this sort of stuff very effectively.
Describing what is good and what is bad on the internet is not always an easy task. However, almost everyone reading this will agree that the following activities are most definitely 'Bad'...
Viruses, Trojans, Spyware, Malware, SPAM (including Forum and Comment SPAM), Malicious Hacking, Malicious Exploits, Malicious Botnets, Harvesting, Scraping, Snooping, Data Mining and the Sharing or Hosting of known Illegal content (not general P2P, but really bad and illegal content). Basically, stuff that shouldn't even be on the internet.
So, how can you best protect your PC (or server) and therefore your Litecoins from the 'bad' guys and all this sort of stuff ? Easy you just need an IP based firewall and a good block list of known bad IP's !
I use PeerBlock (for Windows) or PeerGuardian (for Linux / Mac) and appropriate / relevant block lists from iblocklist.com to protect my Litecoin nodes!
This FREE open source software prevents listed IP addresses from contacting your system and also prevents your system from contacting the blocked IP addresses. Doing this does not affect how Litecoin functions, it just blocks the 'bad' guys! It even helps to prevent them from learning that you are a Litecoin user and will therefore potentially stop them from trying to steal your wallet.
Windows users can get PeerBlock from FileHippo.com See: http://www.filehippo.com/download_peerblock/
or from source See: http://www.peerblock.com/
Linux (and Mac) users should visit: http://sourceforge.net/projects/peerguardian/
and/or read this: https://help.ubuntu.com/community/MoBlock
(which is a useful guide to MoBlock, although MoBlock is now depreciated).
You don't really want to use any of the 'default' Anti-P2P lists, you should get relevant and updated block lists from iblocklist.com
You simply 'Add' the update URLs to the blocking software. I would advise blocking the following lists when running Litecoin:
(1) Spyware (Block)
(2) Hijacked (Block)
(3) Dshield - Anti-DDoS (Block)
(4) Forumspam (Block)
(5) Webexploit (Block)
(6) Hijacked - 2nd list (Block)
(7) ZeuS - Botnet (Block)
SpyEye - Botnet (Block)
(9) Palevo - Worm / Botnet (Block)
(10) Malicious (Block)
(11) Malc0de (Block)
(12) Known 'Bad' Sharing of Illegal Content (Block) i.e. Bad Peers and the other bad ones etc.
Those running windows should (Allow) Microsoft.
You can decide if you want to allow or block: The Onion Router - Tor lists (N.B. That you can easily allow or block this in Windows when using Peerblock). I therefore switch the Tor list off when I'm using the Tor browser bundle on windows, for example.
The Exclusions list is also worth considering as an Allow list for Windows users.
Rangetest, Ads, Bad Peers, Spider, Search Engines, Adservers, Edu and Educational lists and even the Level 1 / 2 anti-P2P lists are also worth considering. Lots of universities etc. are running Litecoin nodes. It's really up to the individual what you want to block and/or to stop your own Litecoin node from connecting to! You can even block entire countries if you want to.
N.B. Rangetest does not currently seem to work properly with PeerGuardian in Linux and causes an update error for me sometimes.
Users with a subscription at iblocklist.com should also block the Spammers list, as well as the Anti-Infringment list. Most other lists are really not very useful for Litecoin, but again its up to you what you decide to block.
I originally wrote a similar guide to be used with the Tor Browser Bundle. See: https://xeronet.primeoptic.net/protector.php
I'm not affiliated with any of these software products or other websites.
So, be safe and protect your Litcoins! Doing this also helps to make the entire Litcoin network safer and slightly faster, for us 'good' guys!
Encrypt your wallets to folks.
Tip Jar - LTC: LXetUzJkeSkRxV8eF7qvTnZ22xm5cYzmoh