VirusTotal is one of the known web services that can detect malware.
Uploading a download URL or downloaded file to this website will alert you to well-known malware or suspicious files. Note, however, that it is not perfect.
I uploaded the Combat Evolved - Halo Mod 1.7.10 jar file to the service and at least VirusTotal says it is safe.
https://www.virustotal.com/gui/file/3d28294d5830427922bfb4871c9822d6007c0df3f623c366671b6458f24a342c
I'm convinced that the easiest and best way to protect your computer from threats is to never download anything from suspicious files or unreliable websites.
Please note that you are always on your own and must exercise due caution.