When I updated to the new version of Steam
It was the December 10th update, rereleased on the 14th due to crash issues.
Hi EmoHobo 
Win32:Evo-gen [Susp] = Suspicious.
That can happen with new(er) files.
If you trust it ( and here you can as you have updated Steam ) you can "Add the file to the scan exclusion list ".
Greetz, Red.
Just received it too.
Had Steam open, and when I opened the Task Manager to test the performance with 60fps videos…
Glad to see I’m not alone on this issue and on being a huge fan of Len and Vocaloids.
Strange. Every time that I open the Task Manager, Avast will tell that some file is suspicious (same Virus).
It already happenned here 2 more times (with files trz7881.tmp and trzA352.tmp).
Off-topic: Rin and Len = best vocaloids.
EDIT: I exit Steam, re-scanned the files that were on Virus chest (no virus detected), restored all of them, started Steam, and no more alerts (No, they weren’t added as exclusions). Also, even after restoring the files, they are still in the Virus chest.