NEW YORK (CNN/Money) - Worms are back in the news, seen in widespread network outages Tuesday afternoon.

How seriously are you taking your own PC security? If even the government and corporations can't keep themselves from being hacked, how can we PC-users protect ourselves?

Software companies are finding holes in their systems all the time -- sometimes because a hacker pointed them out.

Make sure you get all the appropriate patches that your operating system needs. If you're a Microsoft Windows user, get your monthly updates at www.Microsoft.com/security. If you use a Mac, check out updates at www.Mac.com/support.

On top of that you need anti-virus software to fight the viruses and worms that come creeping in off the Internet and a firewall to keep out the weirdos.

"The number one security you can put up is a firewall. A lot of people don't realize that they can have one on their PC, they think they are only for businesses. That's not true," says Michelle Petrovich at the Department of Homeland Security.

For a free trial of a firewall, check out download.McAfee.com or www.Symantec.com/downloads. McAfee and Symantec also offer anti-virus software.

You can also prevent hacking by increasing the security settings on your Web browser, says Petrovich. It may limit some functions on Web sites, but it can protect your computer from being hacked.

To up the security setting on Internet Explorer, for example, check out the TOOLS menu, select Internet Options, Security, and then Custom Level. For other browsers, check their help menu.

You may have heard about the "evil twins" that often attack over wi-fi.

If not, here's how it works. "Basically, an evil twin is someone who masquerades as a hot spot. They send out a stronger signal, so instead of connecting to the Internet via the hot spot, your computer connects to the evil twin. He can take all your information directly," says Richard Rushing, chief security officer at AirDefense, a wireless security software company.

In other words, it's not always the best idea to take your show on the road. Avoid using your laptop in public places where it may be easy for an evil twin to attack and steal passwords and other personal information saved on your computer.

You've got a virus, your computer crashes, and your whole wedding album is gone. Don't go there. Back up your computer files.

These days we're keeping everything on our computers, especially as we link them to our iPods and Blackberries: addresses, resumes, journal entries, music, movies, and priceless photos.

Don't risk losing it all. Experts recommend you buy an external hard drive and some automated backup software to copy the data from your computer regularly.

Viruses and worms are hiding even in the friendliest of places: e-mails, instant messages, and pop-up adds.

The Department of Homeland Security recommends computer users, "Don't download, install or run a program unless you know it's been written by a person or company that you trust."

Be wary of opening any unexpected attachments in e-mail and clicking on any URLs in instant messages. If you have children using your computer, make sure they understand these guidelines.

File-sharing is not just for teenagers. People of all ages are swapping music, movie and other entertainment files over the internet.

Aside from being illegal most of the time, file-sharing also puts you in hacker harm's way.

"Using this technology makes you susceptible to risks such as infection, attack, or exposure of personal information," DHS advises.

There is really no way to know whether the individual you are sharing files with is trustworthy. File-sharers might tack spyware, viruses, and worms onto the files without your knowing. You're best off avoiding the practice altogether.

For more on keeping your data secure, click here.

What can you do if your identity has been stolen? Click here.

Gerri Willis is a personal finance editor for CNN Business News and the host for Open House. E-mail comments to 5tips@cnn.com.