system
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Hello,
I believe someone else has already said it, but I checked on Avast Facebook page and they have replied to some questions regarding this issue as being a false positive. After the last update, I’m able to login to gmail without any warnings. 
From https://www.facebook.com/avast?filter=2 :
Thank you for reporting this. Trojan Horse" HTML:Bankfraud-BYL [Trj] was a false positive, and the detection is already disabled (should be OK in the next VPS). It was falsely detecting Gmail login page in specific circumstances.
As for the new/old gmail layout, it seems to come and go, sometimes I get the new one and sometimes the old and this was already happening for a couple days, but this didn’t seem to make any difference when avast reported the Trojan.
Hope this helps.