Desktop virus scanners are not the only software that will help you scan files that you download, there are several online antivirus engines that will let you upload a file and scan it to see if it contains any virus or spywares.
No Virus Thanks also provides with a easy way to scan files for viruses, however the unique thing about this service is that, once you upload a file it will scan it against 24 Online Antivirus engines simultaneously.
Another interesting feature of this online antivirus engine is that it also allows you to scan files by providing a URL, so if you have suspicions about a software you want to download, you can first scan it and check to see if it is clean, before even download it.
The maximum size of file you can scan using this engine is 20MB, however it can come in pretty handy to scan suspicious files.
[via Life Rocks]