The file Base64.class is reported to be
a "TrojanDropper.Java.Small.c" by Kaspersky Antivirus.
This also holds when the antivirus heuristic (searching
for unknown viruses) capabilities are disabled.
I will post this information to the antivirus manufacturer
as well. However, for the sake of MrPostman users,
check things anyway, in case you took this class from