Specifically with Clam Xav Sentry configured to scan inserted disks.
Please read global comments on this question for an explanation of why desktop apps are being recommended for virus detection on ios devices.
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Does not slow down computer under normal use.
Pro Realtime scanning engine
This feature is called ClamXav Sentry, and this is what really makes this application valuable, it is a real time scanner that monitors changes in files and directories. It does require some setup and configuration to have functioning properly. Ideally you want to include directories where files are downloaded into your system for ClamXav Sentry to monitor. Alternatively, you can make it monitor your whole home folder if you don't know what you're doing.
Pro Option to build/configure your own ClamAV engine
You can roll your own engine if you wish.
Pro Free customer support
Customer support does not cost anything other than a single purchase of the app itself.
Pro Frequent & free malware database updates
Frequent updates means the user is more protected from current attacks.
Pro No yearly subscription fees
Clam Xav has a one time cost of $29.95. There are no other fees associated with the app, since it is purchased, it is yours to use for as long a s you like.
Con Does not scan memory
There is no way to scan the memory of ones device with this app, leaving an avenue of attack since the app is not able to detect anything amiss in the memory itself.