A friend of mine recently complained about how slow her laptop was, so slow that she could barely use it.

I looked at it, and she had pop-up ad after ad continually popping up. She had four different toolbars in her web browser, usurping screen space. And she had a half dozen programs automatically loading at boot-up that she didn't use. 

Her system was infested with malware. Is yours? Chances are even if you haven't experienced this, a family member, a friend, or a coworker has or will. Here are some tools and tips that can help.

Malware has different definitions. One is any software that has malicious intent. Another is any software you don't want, didn't ask for, and don't need. Other related terms include spyware, bloatware, phishing, zombie, worm, and trojan. Sometimes the term virus is used as a catch-all for malicious software, though it more correctly refers to programs that replicate, like biological viruses.

At its worst, malware can capture personal information such as bank logins and Social Security numbers, stealing from you. Other malware sets you up as a relay station for sending out phishing schemes to scam others. Still other times, as with my friend, you're just bombarded with ads and unwanted software add-ons and programs.

In a study it did recently, Microsoft found that 7.8% of the computers it polled were infected by malware, though that figure rose to as high as 44% for some countries in Asia and Africa. According to Tim Rains, director of the company's Trustworthy Computing section, the reason for these high numbers is the relatively low use of security software.

If your system is infested, you have various options. You can pay for heavily promoted services such as My Clean PC (www.mycleanpc.com). You can pay a local computer repair shop to clean your PC for you. (Office supply stores such as Staples sometimes have promotions in which they'll clean your PC for free.)

Alternatively, you can clean up your system yourself using software that's free, with donations typically requested or with beefed-up pay versions of the software also available. Recommended programs include Malwarebytes (www.malwarebytes.org), Spybot Search and Destroy (www.safer-networking.org), and Ad-Aware (www.lavasoft.com). You can use one, two, or as I did all three to clean up a system.

But why not keep your PC clean and running fast before you have problems? There are both free and low-cost ways to do this. Some Internet service providers offer subscribers good protection against malware as part of their subscriptions. But not all do, and some people get their Internet access through WiFi hotspots.

The most robust and convenient protection against malware comes from the fee-based security suites of top security companies such as Symantec's Norton 360 (www.symantec.com), the best security software I've come across. The typical annual subscription cost is $89.99, though at the time of this writing Symantec was having a sale, dropping this to $49.99.

As with similar pay services such as Intel's McAfee All Access (www.mcafee.com), they protect not only against malware but also malicious websites and email spam.

Free services can be highly rated, a good option as well. Recommended programs include AVG Free (www.free.avg.com) and Avast Free (www.avast.com). Typically, such programs are better than the software that comes with Windows--Windows Defender with Windows 8 and Microsoft Security Essentials with Windows 7--though these included programs can also protect against most threats.

It's also important to keep up to date. Older programs and operating systems are more vulnerable to attack. With whatever security software and operating system you're using, enable automatic updates. Keep any pay security subscriptions you have up to date as well.

With programs that don't update themselves automatically, you can periodically check manually for updates, usually through the help menu. Or you can use a program such as Secunia Personal Software Inspector (www.secunia.com), which checks for and installs updates for you.

Regardless of the precautions you take, sometimes things just go wrong. If you have photos, tax records, or other data on your computer that you can't afford to lose, the often repeated and often ignored advice is to back up important files.

Options include using an Internet backup and file sharing service such as Dropbox (www.dropbox.com) or Google Drive (www.drive.google.com), a USB flash drive, a rewritable optical disc, an external hard drive, or a backup tape. It matters less what you use than that you use such a service, ideally more than one in case of glitches.