Proprietary software tends to have malicious features. The point is with a proprietary program, when the users don't have the source code, we can never tell. So you must consider every proprietary program as potential malware. ↗
It is always right to detect a fraud, and to perceive a folly; but it is very often wrong to expose either. A man of business should always have his eyes open, but must often seem to have them shut. ↗