What is it?

ashMaiSv.exe is an executable file that is included with the avast! anti virus program

What does it do?

Both the virus database and the program itself can be updated automatically. The updates are incremental, i.e. only the new or missing data are downloaded, thus reducing the transfer heavily. The typical size of a virus database update are tens of KB, the program update usually has hundreds of KB.

If your Internet connection is persistent, the updates are performed completely automatically in fixed time intervals. If you connect to the Internet only occasionally, avast! watches your connection and tries to perform the update when you are online.

More info:

http://www.avast.com/