Same issue seen here for the last approx. 2 or 3 months, on every manual Vdefs update when the log was pulled down. Not quite every time, but probably 90% observed log, and 100% of those observed, look like yours. Most automatic, self-updates occurred without observation. Hope there is an easy explanation.
Here's my example, the latest one that I saved for reference:
2013-12-11, Thurs., ~10:30 PM CST - elrond > Updating VPS files, last update 13121001, prgm. is still v8.0 (400005):
Connecting to repository
http://download.ff.avast.com/mac/vpsmacDownloading vpsmac.lat...
Downloading vpsmac13121001.inf...
Downloading vpsmac13121100.inf...
Downloading vpsmac_13121001_13121100.dif...
Downloading vpsmac13121100.inf...
Downloading vpsmac13121101.inf...
Downloading vpsmac_13121100_13121101.dif...
tar: install/update.sh: Not found in archive
tar: Error exit delayed from previous errors.
+ RAW='/Library/Application Support/Avast/files/Setup/filedir/vpsmac.raw'
+ '[' '!' -f '/Library/Application Support/Avast/files/Setup/filedir/vpsmac.raw' ']'
+ VERSION=13121101
+ '[' -z 13121101 ']'
+ FILES_DIR='/Library/Application Support/Avast/files'
+ '[' -d '/Library/Application Support/Avast/files/defs/13121101' ']'
+ mkdir -p '/Library/Application Support/Avast/files/defs/13121101'
+ '[' 0 -ne 0 ']'
+ tar -x -C '/Library/Application Support/Avast/files/defs/13121101' -f '/Library/Application Support/Avast/files/Setup/filedir/vpsmac.raw'
+ '[' 0 -ne 0 ']'
+ echo '[Definitions]'
+ echo Latest=13121101
+ exit 0
Connecting to repository
http://download.ff.avast.com/mac/AAFMDownloading AAFM.lat...
Package AAFM is up to date.
install/update.sh
No program update available.
------------ The above has always been the last line, ever since Oct. 2, 2013 when v8.0 (40005) replaced v8.0 (39905) ---------------
- running Avast Free Antivirus with 224 days to go in the trial registration, Program = v8.0 (40005). OS X 10.7.5 (Build 11G63) Mac mini (mid-2011) with Intel CPU and upgraded RAM 4 GB, 200+ GB free on system partition, HDD.