This is why:
License Agreement on Use of an AVG Anti-Virus Free Edition
' The GRISOFT Company through this License Agreement grants to you non-exclusive and non-transferable rights thereunder in respect of using a copy of the computer program for a service life thereof, i.e. for a time period throughout which GRISOFT shall maintain and make available an updated version thereof. You may install (download) and use only one copy of the program designated for protection of exclusively one personal computer, notwithstanding as to how many times you download the program and how many times you accept the License Agreement. You must not use the program in a network or on more than one computer. This particular software version is distributed free of charge, therefore, the applicable license is only granted for home use thereof. In case of this free version, the program is not subject to any guarantees, and the user has no right to any technical support whatsoever. '