Expired Antivirus Protection Just as Bad as None

Credit: Oleksiy Mark/ Shutterstock

(Image credit: Oleksiy Mark/ Shutterstock)

Expiration dates aren't just for food. Antivirus programs can also go stale, and when they do, they're almost as useless as having no antivirus protection at all, according to the latest edition of a twice-yearly Microsoft study.

In its Security Intelligence Report 17, released today (November 18), Microsoft found that computers with expired antivirus protection were only slightly less likely to be infected with malware than computers with no antivirus protection at all, and almost four times as likely to be infected as computers that had up-to-date antivirus protection. 

MORE: Best PC Antivirus Software 2014

The study in SIR 17 was performed on "non-domain" computers, those that aren't controlled from large enterprise administrative servers. Non-domain computers include almost all consumer, and most small-business, PCs.

Microsoft found that PCs with frequently updated, real-time antivirus protection had only a 0.6 percent infection rate. By comparison, 2.2 percent of computers with expired antivirus protection were infected, as were 2.4 percent of computers that had no antivirus protection.

Those look like small numbers, but Microsoft also found that 10 percent of non-domain Windows 8 and Windows 8.1 computers were running expired antivirus protection.

How do PC owners end up with expired antivirus programs? Often, newly purchased machines come with a month or so of free antivirus protection, and owners let that protection expire without renewing or replacing it.

Supporting this thesis, Microsoft found that the month of January 2013 had the highest percentage of computers with active antivirus software, likely correlating to people buying new computers over the holidays. After January, the percentage of actively protected computers trails off as these trial antivirus programs expire. 

"Computer users who run expired or out-of-date security software may believe that it continues to provide an adequate, if less than optimal, level of protection. ... This belief is misguided at best," according to SIR 17. 

The report also found that expired trial antivirus programs may actually put people at even more risk. Microsoft found that computers with expired antivirus programs from a certain antivirus vendor (identified only as Vendor A) were even more likely to be infected than people with no antivirus protection at all. 

"For these vendors, the existence of so many expired trial versions has a significant impact on their ability to offer protection," reads SIR 17.

Jill Scharr is a staff writer for Tom's Guide, where she regularly covers security, 3D printing and video games. You can follow Jill on Twitter @JillScharr and on Google+Follow us @tomsguide, on Facebook and on Google+.

Jill Scharr is a creative writer and narrative designer in the videogame industry. She's currently Project Lead Writer at the games studio Harebrained Schemes, and has also worked at Bungie. Prior to that she worked as a Staff Writer for Tom's Guide, covering video games, online security, 3D printing and tech innovation among many subjects. 

  • firefoxx04
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  • Zachasaurs
    dude i just have Microsoft firewall and it keeps me safe and without viruses and its free best one possible
  • Silent Ricochet
    Pretty funny coming from a company that relies on you to manually update Windows Defender every day. (Unless you have automatic updates on. Which is honestly annoying).
  • r0llinlacs
    Lol. "Anti" virus.
  • yumri
    @Silent Ricochet in short new nasty viruses come out almost every day so Windows Defender has a update that often but also it is probably gathering infomation about how well it works on your machine sending what is in the "system" screen, what version of windows defender it is, and then it will give you the update for windows defender as the first 2 things are gathered by any and all software to make sure they give you the correct update(s) even though a little intrusive.
  • mdd1963
    Microsoft's 'firewall' is often referred instead to as an 'open door'; anyone tried/tinkered with Personalfirewall 7.0? (Seems easy enough so far; nonintrusive, yet informative little popups every time something 'new' occurs, inbound or outbound, for those that are curious and/or paranoid!)
  • dstarr3
    I use Avast and Malwarebytes. Free versions of both that are perfectly functional. And these are the least resource-hungry of all the antivirus/malware solutions out there. I don't see why people use need or use anything else.
  • r0llinlacs
    The best anti-virus is always yourself (if you're competent). Best of all, it doesn't horrendously tax your hardware, or spy on you.

    Signed, 15 years virus free with MeMyself&I AV hardware
  • Somasonic
    @r0llinlacs - if you have no AV software how do you know you have no viruses?

  • r0llinlacs
    It's not that difficult to see what's on your computer. I can see and check everything from files to processes to registry entries to program/file network usage to everything else you can think of. If you know what viruses do, it's easy to spot them without anti-virus.