On this screen, you can adjust the basic sensitivity, which determines how thoroughly files are scanned, and also the heuristic sensitivity.

As well as the standard process of scanning for known malware infections, avast! also performs a heuristic analysis to identify potential, but as yet unknown malware. This is done by looking for certain characteristics that may be a sign of a potential infection. By clicking on the orange bars, you can adjust the level of heuristics sensitivity to Low, Normal or High, or you can turn it off completely. Increasing the sensitivity, increases the chances are of detecting a virus but also the likelihood of “false positives”.

If you find that a large number of clean files are detected by avast! as suspicious (“false positives”), it is possible that the heuristic sensitivity is set too high. Reducing the heuristic sensitivity should result in fewer files being reported as suspicious, however this also reduces the chances of a real virus being detected.

If the box “use code emulation” is checked and avast! detects some suspicious code in a file, it will attempt to run the code in a virtual environment to determine how it behaves. If potential malicious behavior is detected, it will be reported as a virus. Running the code in this virtual environment means that if the code is malicious it will not be able to cause damage to your computer.

You can adjust the basic scan sensitivity by checking or unchecking the following boxes:

  • Test whole files (may be very slow for big files) – checking this box will result in scanned files being tested fully, not just those parts of a file which are normally affected by viruses. Most viruses are normally found either at the beginning of a file, or at the end. Checking this box will therefore result in a more thorough scan, but will also slow the scan down.
  • Ignore virus targeting – if this box is checked, all files will be tested against all of the current virus definitions. If it is not checked, files will be tested only against those viruses that target the particular type of file, for example, the program will not look for viruses that normally affect files with a “.exe” extension, in files with a “.com” extension.

By checking the box “Scan for potentially unwanted programs (PUPs)”, you can also scan for programs which you may have downloaded unknowingly, typically programs that are used for advertising, or collecting information about your computer or internet use.

By checking the box “Follow links during scan” you can ensure that the targets of any file system links are also scanned for potentially harmful content. If this box is checked, the content of any folder to which you would be redirected from a folder which is being scanned, will also be scanned.