First of all, read the Frequently Asked Questions about amiga viruses. Second you have to start an antivirus program from a clean scource. That means you have to boot your Amiga from a floppy disk. Virus Help Team have made some floppy disk that you can download, with all the latest antivirus programs and library's xvs.library v33.47 they need, and they are all clean and ready to use, these floppy disks are packed with 'Disk-Masher' (dms) and 'Amiga Disk File' (adf), so you have to unpack the archives first. The second this is what Kickstart (KS or OS) you use, and this is very important.

Here is what antivirus programs you can use: