1) Virus detection : Normally, a virus detection program checks the integrity of the binary files.The program maintains a check sum of each file. A mismatch in it indicates virus. Some program reside in the memory and continuously monitor certain memory and I/O opera tions for guarding against any suspicious behaviour.
2) Virus removal :A generalised virus removal program is very difficult to imagine due to multiplicity of the viruses and the creativity with which they are constructed.However, for some viruses, bit pattern in code can be predicted. In this case virus removal program scans the disk for the patterns of known viruses. On detec tion, it removes them. But, if the virus has already damaged data, then recovery of data is almost impossible.
3) Virus prevention: User cannot cure the data (recover) after viral affection. Hence the best way is to prevent viruses. For this must buy official, legal copies of software from reliable stores or sources. One should be extremely careful about picking up free, unreliable or illegal software. Frequent back-ups and running of monitoring programs also help in detection and thus subsequent prevention of different viruses.