Activity monitoring programs may be more trouble than they are worth because they continually ask for confirmation of valid activities. A checksum is a unique number generated from the bytes within a file. Any changes made will generate a checksum different from the one previously calculated. Checksum is one of the most reliable methods of virus detection. Scanners, as the name implies, scan files for viral signatures, bits of computer code that exist only in specific viruses.
Scanners have the advantage of being almost invisible during operation.
Their biggest disadvantage is they look for specific bits of computer code, so they can detect only those viruses listed in their databases. Scanners, because of their almost transparent operation, have become the most successful type of AV program on the Mac. To simplify updating the programs' virus databases, most scanners permit downloading of new databases from the manufacturer's web site. Virex 5.7.1 Datawatch Corporation's Virex is an AV program that uses both the checksum and scanning detection methods. Datawatch has made the checksum and scanning techniques easy to use with a simple and efficient user interface.