Now is the time — while you’re getting everything set up just the way you like it — to take some steps to keep your new machine clean and free of malware. Here is what you need to do before you do anything else.

Check your firewall settings
Do this before you even connect your computer to the Internet. Firewalls prevent certain unwanted traffic from reaching your computer, including worms that spread through network connections. New laptops and desktops with Windows Vista (and, come Oct 22, the next version of the operating system, Windows 7) and netbooks using Windows XP SP2 or higher have a firewall that is built in and turned on by default. You can make sure all is well by going to the Windows Security Center, clicking Start, then Control Panel, then Security Center and Windows Firewall.
Mac users can check and adjust their firewall settings by clicking on the Apple icon and going to System Preferences and clicking on Security and then Firewall. At a minimum, choose “allow only essential services.”

A better option is to select “set access for specific services and applications” and play gatekeeper, allowing programs to connect as you need them, said Rich Mogull, founder of the security consultant firm Securosis.

Update your software
Even though you have a new machine, chances are that security fixes have been issued since the manufacturer loaded the software, so you will want to download those as soon as you get online.
Your new PC may prompt you to check for updates from Microsoft, but, if not, open Windows Update by clicking the Start button, then All Programs and then Windows Update. On the left pane, click “check for updates.” (For more information about Windows Security, see microsoft.com/protect.)
To help you keep Microsoft products up to date, Windows will prompt owners of new machines to sign up for automatic updates. You will see a screen asking if you want to “Help protect Windows automatically.” Choose the first option, “Use recommended settings,” so you get everything and don’t have to worry about it again.

Barring an urgent problem, updates come out on the second Tuesday of the month. To schedule exactly what time your updates are installed — say at 3 am, when you are asleep — open Windows Update and select Change Settings and make your choices. This is also a good time to turn on the Internet Explorer Phishing Filter, which can help keep you from turning over personal information to the wrong people.
For Mac users, your computer will automatically check for updates once a week. If you are a paranoid person, have it check more frequently by clicking Software Update in the System Preferences panel and then choose Daily.

Add security software
Firewalls won’t help fend off viruses or Trojan horses that can come through e-mail messages, Web sites and pop-up ads. Given the frightening number of malicious programs that aim for Windows PCs, owners of these machines really need to use some security software. There are several free antivirus programs, like AVG 8.5 Free, Avast Antivirus and the forthcoming Microsoft Security Essentials, so even penniless students have no excuse to go without. Note that Vista comes with Windows Defender, which blocks spyware and pop-up ads, and that program can be downloaded free by Windows XP SP2 machines.

Since a lot of malicious programs now come through Web sites, you will also want to use one of the many free tools available to help you avoid malicious sites. Microsoft’s newest browser, Internet Explorer 8, will warn you if you try to visit sites it deems unsafe, deceptive or carriers of a common Web attack type called “cross-site scripting” attacks. Other browsers, including Chrome, Firefox and Safari, also warn users about potentially unsafe sites, using a blacklist kept by Google. There is also McAfee’s SiteAdvisor, a free add-on for the Internet Explorer and Firefox browsers (the latter works on both Windows and Mac), that shows site reputation information within search results pages, including warnings about potentially dangerous sites.

There are few malicious programs that aim for Macs, so an antivirus program isn’t essential at this point. That said, some Mac experts think that the days of peace and security for Macs may be waning. There have a been a few Trojan horses recently, and some Web attacks don’t care which operating system you use. If you frequent file-sharing sites, or your employer requires it, buy a Mac antivirus program.
Sort out the applications

New Windows PCs typically come loaded with all kinds of third-party programs, many of which you will never use.
“In a lot of cases, that’s extra software that might have vulnerabilities” that hackers could exploit, says Chad Dougherty, a vulnerability analyst at the CERT Program at the Carnegie Mellon Software Engineering Institute.
To avoid problems, eliminate the programs you don’t need by clicking the Start button and choosing Control Panel and then Programs to see a list of what is on your machine. Select unwanted programs and then hit the Uninstall button at the top of the program list.

Then sign up for automatic updates from the makers of any software you intend to keep — or that you later install yourself, for that matter. To help you make sure you have checked out everything, download Secunia PSI, a free tool that will help you make sure that all the programs on your PC get security patches.
Speaking of that, always be careful about which software you install from the Internet, whether you have a PC or a Mac. These programs can contain vulnerabilities, and pirated programs and random add-ons may be outright malicious.