LordBucket's tips for not getting hacked:
1) Do not give out your IP.
2) Do not log into the GS
3) Auto-clear everything you do. Note that it takes some practice to get the timing right. Start now, and make it a habit. Don't wait to look up the auto-clear tutorial when you have a bank account you'd like to steal from.
4) Only connect to other machines when you have either an instant IP-change, or money to pay for one available. If your next one is available in 24 hours, don't connect to any external systems for 24 hours. Only log in to collect money from slaves. At the end of each play session, virus scan and change your IP.
5) Only collect income from slaves during the period between having switched your IP and having connected to any external system. Once you've connected to an external system the possibility exists that your local log is being watched. Never collect money from slaves when this possibility exists. It is better to risk losing some income from a slave that cleared your virus than to risk losing your entire bank accoutn because someone was camping your log.
6) Tell noone what level waterwall or firewall you have. If they know, they can consult the list to determine exactly which npc system you need to get your next upgrade.
7) Create at least three bank accounts. When collecting money from slaves, favor putting the money in the bottom-most accounts on your list. Favor doing risky things with the top-most accounts on the list. When paying for things, the game will withdraw money from the top of the list and work down. Never under any circumstances do a transfer to or from the accounts you wish to keep secure.
Don't delete old firewalls. Keep a great big pile of all of them of various levels. Rumor has it that firewalls somewhat increase the difficulty of cracking your password. If after 5 attempts someone still hasn't cracked your password, they might get bored and move on. I can't confirm that this is true. It might be a viscious lie. But it might be true. If you have the space, you might as well use it.
9) Hold onto as many old versions of absolutely everything you can possibly fit room for. If your hard drive is full, that means less space for people to upload a virus to. The more files there are, the longer and more log entries it would take for someone to delete you. Having only a single waterwall makes it tempting to hide or delete it, which can massively hurt you. If you have 10 waterwalls of varying levels, if someone deletes one, then you only have to replace that one, not start over. And it might not be worth their time to delete all of them. This applies to other software as well: if you have only one seeker or one antivirus, it's tempting to hide or delete them. Have redundant copies of everything.
10) Hide your own viruses that you have on your local machine to prevent other people from installing them. If someone is going to install a virus, at least compell them to take the time to upload their own.
11) Keep a browser tab on your local log. Clear it after every action you take, and refresh regularly even when not doing anything to check for changes. Also, leave several lines of text with a fake IP or fake bank account transfer in it. It faster to mouse select all and press delete to completely clear a log than it is to selectively delete only a single line, or to copy and paste rather than delete. Having that one entry lures a hacker into taking longer to clear the log of their visit. Update the timestamps on these fake entries periodically to make them look recent. If someone sees that you're online right now, they wait and come back later, by which time you will have changed your IP.
12) Take note of the used/available space on your local drive after every file you add or remove. Write it down. If it changes, and you didn't do anything, that means that somebody else did.
13) Whenever connecting to a player owned system, after clearing the log and before doing anything else, sit and watch the log, refreshing it every couple seconds for a little bit in order to find out if that player is presently logged on.
14) Create a text file on your local drive asking for play advice from people who hack you. This gives them an opportunity to feel smarter than you, and by satisfying this basic desire, they may feel less need to feel powerful by deleting your files. By implying acceptance of their presence, you also confirm in their mind that they are in the dominant position, and that you are a submissive male in their pack, which may tend to encourage them to feel protective rather than exploitative of you. It also encourages them to waste time and create an extra log entry by replying to you, in which case you have a better chance of noticing and getting their IP.
Good luck.