Hello!
So I have this schoolwork where we´re going to look up some facts from different anti-virussoftwares that are out there. My group chosed avast! to work with and I got the subject to look up how an anti-virus works.
So could anyone explain for me a little bit how an antivirussoftware works?
Sincerly.
… And you can skip “the software search for viruses”.
I want the technical data of it.
Hello Rxl
For beginning you can read avast! Help (it’s very usefull document 
)
Here’s an extract from one page in the help
It describes the methots of scanning.
Quick Scan. Only the possibly dangerous files are scanned, according to their extension. It means that the files with extensions EXE, SCR, COM, DOC, etc. are scanned. Within the file, avast! looks only for those viruses that infect the corresponding type of file. It means that macroviruses are not searched for in EXE files etc. Standard Scan. Only the possibly dangerous files are scanned, according to their content. The file extension is ignored. Again, only the viruses corresponding to the particular file type are searched for. Thorough Scan. All files are tested, against all viruses.
You can also do a forum search. I’m sure that you will find a lot of information here in the forums
Besides doing your homework maybe you’ll discover how useful and protective avast! could be and joing the gang 8)
Wilders forum is a good place to find general info too 
Like XMAS said, the help file is very useful.
Other then that I would reccomend Google (many antivirus reviews out there), and if you have any particular questions I am sure the avast gang would be happy to help.
Good luck on the report.
There really is nothing like practical experience of installing the program and using it, checking each of the various providers and how they can be tweaked, avast is a very configurable, flexible anti-virus.
I have this schoolwork where we´re going to look up some facts from different anti-virussoftwares that are out there. and I got the subject to look up how an anti-virus works.
For the most part anti-viruses use known signatures of viruses in order to detect them, Virus Pattern Signature files (VPS), some also use Heuristics, looking for suspicious activity/patterns, etc.
avast generally uses the VPS file to detect viruses except for the email scanning when it also uses Heuristics. There are two broad types of scan: on-access (often called resident) scanning, where a file is scanned when a program wants access to it, so before the file is executed it is scanned; the other is called on-demand, where you the user initiate the scan and there are different ways to do this.
In some of the resident scanners, avast! also uses a means of scanning the files from the internet and email before they are actually saved on to your HDD or email inbox. So if an infected file is found it can be deleted before it is saved to the HDD or inbox. This is better/easier than having to try and remove the file once it has been saved to the HDD or inbox.
Good luck with your project.