The Economist ran a 10 page special suppliment on cyber security, mostly hand wringing about how little security we have.
They have a point there. Most computers run Windows and Windows is like swiss cheese, full of holes. Any Windows computer on the internet can be hacked, from the net, and quickly. Bill Gates has hung all our dirty laundry out to dry in the sunlight, where anyone can see it.
For instance, those electronic medical records that Obama stuck us with. They are all visible on the net to any competent hacker. For instance, when you apply for a job, HR can access your medical records and put the kibosh on hiring you if they see you as a high cost patient on the company medical plan. And there is nothing you can do about it, your doctor puts your medical records on the computer whether you like it or not, and there you are, hung out to dry. Note: Don't tell your doctor about suicidal feelings, mental problems, anything that might be used against you, either at trial or at a hiring decision.
Things you can do. Use good passwords. Avoid passwords found in dictionaries, they have all been cracked. Passwords like sunlight, tornado, U.S.Grant, hunter, rapids, bulldozer are all precracked. Use long passwords, longer is better. Use mixed case (some caps, some lower case) and digits. For instance Torino69 is stronger than just plain torino. ByTheRocketsRedGlare is stronger than usemgr.
The experts will tell you to use different passwords for each thing (account) that you log into. Good advice, but tough to follow. No way can I remember and keep straight 20 odd passwords for the 20 odd accounts I own. I do use strong passwords and that's about it.
Avoid Windows. Use Linux, or Mac or even MS-DOS. By the way, there is a market opening here, for an OS as user friendly as Windows without Windows uncounted security holes.
Never click on an email attachment. Even on email from a well known friend. The friend's machine may have been hacked, and the hackers always take away the address book. Attachments, ESPECIALLY .doc and .xls (Word and Excel files) can contain hostile code that infects your machine with all sorts of horrible stuff.
Keep your machine off the internet as much as you can. Powering down takes it off the net, and saves electricity. Powering down at night might save you a nasty virus or invasion by a botnet.
Run an antivirus program at least once a month.
Don't let anyone stick strange thumb drives in your machine. They can contain virii or worse that will infect you machine within seconds of plugging the thumb drive into a USB port.