What's new in avast! version 4
An important improvement is the support for new archives. avast! fully supports the following archives now: ZIP, ARJ, RAR, MIME (e.i. binhex, base64, uuencode etc.), CAB, TAR, GZIP, including the SFX variants (i.e. executable files containing given archives). The new kernel is able to scan alternative streams on NTFS partitions as well.
Big care was taken to make sure that files of arbitrary length can be tested - avast! internally uses 64-bit numbers for any file sizes, i.e. the file size is not limited to 2 or 4 GB, respectively.
More:
http://www.avast.com/i_idt_1019.html------------------------------------------
What's new in avast! version 4.1
Support for new archives and packers
The scanning engine of avast! 4.1 adds support for a new set of file archivers and packers of executable files. Relatitely wide archive support of avast! 4.0 was extended with new support for ACE, ARC, ZOO, BZIP2 a Win32 EXE packers UPX, PeShield, PeProtect, AsPack. A change has been also made to the CAB unpacker which should now be considerably faster and which is now available even in the Home Edition.
More:
http://www.avast.com/i_idt_1392.html