I try to test this theory but running UPX on the Netbus trojan.
I uses the UPX to compress Netbus.exe to netbus-upx1.exe
After scanning the NetBus.exe on 32 Anti Virus program. Out of 32 AV, 31 of them detected as NetBus trojan.
So u know that some anti virus can be bypassed. As NetBus is a very old and famous tools, many well-known Anti virus vendors had already added the variants. But you can still try to "compressed" other malware to see if they can bypass "signature-based" anti virus programs.