AVG security software uses a range of techniques including heuristic analysis to spot potential threats. Heuristic analysis is about spotting whether a file fits the pattern of a threat, even if it's not already on a virus blacklist. Although you can switch off heuristic analysis, in most cases the benefits of using it should outweigh the drawbacks.
Heuristic analysis is a technique some security software uses to spot a virus or other malicious software that hasn't previously been detected by the software (on any user's computer). This is useful with new viruses because another major technique, checking files on a computer against a list of known rogue files, won't work in this situation. Heuristic analysis instead involves looking at the characteristics of a file such as its size (which may match a previous copy of the virus under a different name) or its file type, which may not match the file's claimed purpose. Security software can also perform heuristic analysis by opening or running the file in a secure section of the computer so that it can see what the file does, without the worry of it doing any damage.
Changing the Settings
AVG software enables you to switch heuristic analysis on or off using the settings menu. The precise instructions vary across AVG's range, but generally you'll need to click on the "Tools" option in the software and then select "Advanced Setting," look for mention of heuristic and check or uncheck a box. Note that some more comprehensive AVG packages may have separate settings, including whether or not to use heuristics, for different components. These could include file scanners, e-mail attachment scanners and Web link scanners.
Switching on heuristic analysis gives you an added layer of protection because it may catch previously undetected viruses. This can be particularly important as it's possible security experts may not yet have figured out the best way to undo the particular damage caused by a new virus. Although heuristic analysis still works by following set rules, these rules are more detailed than a simple blacklist of rogue files, and the effect is a bit closer to using intuition.
There are at least two reasons for switching off heuristic analysis, both of which may not outweigh the benefits. One reason is if the software is causing problems by repeatedly labeling legitimate files as potentially compromised, known as a false positive. Whether AVG does this too often is disputed and may be a matter of personal experience. The other reason is if using the feature slows down your computer by extending the time it takes for file scanning to run. As heuristic analysis is only one part of the operations security software performs, it's unlikely to make much noticeable difference.