Usually if we download free software from public file hosting service website, it may contain some virus or keylogger. If you run the program without scanning, it leads to problem in your computer. So it is necessary to scan your files before you run or open.
For scanning purpose, you don't need any anti virus but Internet.
VirusTotal.com will scan your file and give reports about the file.
Scan files for Virus and Keylogger in Online for free-VirusTotal.com
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