Changed files
There may really be a large number of reasons for a change in a file. Also the operating system itself lives "its own life" and uses the files very intensively. Each start-up of a program or editing of a document results in a track, which will be detected, and annouced by AVAST32. Here it is your turn to decide, which change is valid and which is not. For example, a change in text files will be caused by you ninety-nine per cent of the time, while a change in the COMMAND.COM file will be caused ninety-nine per cent of the time by a virus. Please, notice that nothing is one hundred per cent sure, which applies to the whole area of virus problems. The other types of files are situated between the two above specified extreme examples. For example, it is really difficult to say about the documents of the Microsoft Word program (*.doc) why they have changed. The cause may have been you, by simple reading the content, or the "macrovirus" which attacked the document in question.
Nevertheless, it generally applies that if an executable program (extensions exe, sys, dll, bin, vxd, scr,...) is infected, the change is much more suspicious than in the case when a document or data file have been changed. But be careful, even here you may face some exceptions.