There could be a simple explanation why Trend Micro’s HouseCall Free Online Virus Scan won’t run, but it could also be a sign that your Windows operating system may need to be reinstalled.

As a general rule, when an antivirus program or any malware removal tools won’t run, that failure could be a positive sign that your system may be infected. This holds true regardless if you are trying to run an “installed” antivirus program or a “run-time” version of one such as HouseCall.

Unless you had installed a third-party antivirus program on your Windows 10 computer, you would rely on Windows’ built-in antivirus called Windows Defender (which used to be available separately as Microsoft Security Essentials under Windows 7).

You may wonder why I would claim your Windows operating system may need to be reinstalled if your regular antivirus program still works?

An intelligently designed piece of malware could disable your antivirus program (the one that it managed to bypass to get installed in the first place). The new infection could result in a blatant failure of your antivirus program, or it could be more subtle such as disabling the program’s ability to get new virus-signature updates.

Without new updates, even an otherwise functional antivirus program would not know the signature of the offending infection and therefore not recognize that a specific virus might be present.

Therefore, the absence of “bells and whistles” announcing that your computer has malware infections does not mean your system is not infected. It is a good idea to run Trend Micro’s HouseCall Free Online Virus Scan, even if you have other protection in place!

If you cannot get HouseCall to run correctly, you may not want to trust your computer since you would not have any confirmation that it is in fact clean.

As I mention under free software, in my experience the best free (installable) antivirus solution for Windows is Bitdefender Antivirus Free Edition.