Can you tell us why you think there might be a virus? Have you tried booting into Recovery and wiping the cache partition? That often helps with performance issues. Reset: Samsung Galaxy Note 3 | T-Mobile Support
Not sure if there is a virus or not. Been running a little sluggish lately. I have never bored into recovery and wiped the cache partition. Will that have an effect on my apps? Phone? Reset everything? How do I do that?
Wiping the cache partition only deletes temporary system data. Personal data and settings are untouched. The steps from the T-Mobile site should still work for your AT&T version.
I use Avast for anti-virus and Malwarebytes for malware. But if you download only from the Play Store or Amazon, you shouldn't have any viruses or malware. If it happens, it would be all over Androidland.