What about viruses in software?
The shareware industry has an excellent track record providing products that have been checked thoroughly for viruses. Shareware authors, webmasters and other system operators carefully scan programs for viruses before offering them to consumers, so a shareware program will often have more checks made on it than regular commercial software. In recent years, very few shareware websites host files; most are linking to the shareware files back on the web sites of the authors, so you're getting files directly from the source. The few sites that do their own hosting are nearly all quite large, and scan their collections regularly and carefully. When in doubt, download directly from the authors' web sites.