Cleaning a disk of file viruses involves deleting the virus code from the infected file, while cleaning a disk of boot-sector/partition-table viruses involves deleting the virus code from the respective sectors and copying the boot programs back to their original space.
Although all this seems easy, the actual process is very complicated, and sometimes drastic measures have to be adopted to delete viruses, such as deleting infected files or formatting disks.
Anti-virus programs are mainly of two types:
- Scanners
- Antidotes
Scanners scan the hard disk or floppy disk and detect many viruses; for example, the program VirusScan by McAfee Associates. These programs normally check for a known number of viruses. Figure 2.5 shows the starting screen of McAfee virus scanner for Windows NT.
The scanner checks all the files on the disk that you specify for viruses and reports if it finds any. Then you can either delete the infected file or let McAfee clean the file. The scanning process is shown in Figure.
The Starting Screen of McAfee Virus Scanner
Antidotes destroy viruses which they are programmed to detect. Examples are CPAV from Central Point and Norton Anti-Virus from Symantec Corp and McAfee.
McAfee Virus Scanner in Operation
Some virus scanners reside in the computer's memory and check for the entry of a virus after every I/O operation. On detection of a virus, a warning is displayed and all further operations are suspended.
Examples are Smartdog and UTRes.
However, these days most anti-virus software perform scanning as well as eradication of viruses. A typical example of this category is Norton Anti-virus.