Same issue here... which the avast team should easily be able to reproduce if necessary.
Windows Updates (I'm on Win7SP1x64) for DotNet Framework 3.5.1
I believe the specific update was kb2943357 (but it could have been kb 2937610).
The update was placing a plethora (20? 30? 40? who knows) of .TMP files on the hard drive, which were picked up as suspicious EVO-GEN. Avast defs 14-08-12-0
There was no practical way to capture and upload all of these files for F/P testing. There was also NO simple option to IGNORE these files, as I wanted to do (choices included fix, delete, repair, quarantine). Since these were directly from Microsoft Update, I believed they were safe, and wanted to install them.
Basically, I believe/hope I x'd out each of the warning windows... and that doing so would "ignore" the warning, and allow the files to download/install. I'm only hoping I didn't miss any... Windows Update indicates the installation was successful... but what if I clicked ignore on say, only 39 out of 40? Could that still show as "successful"? Would it be wise to try to re-install the update?