My NIS stops updating at block 879713 (~88 days), does anybody know what i can do?
Are you running 0.6.84?
macOS Sierra 10.12.3
NEM Community Client (NCC)
0.6.84-BETA
NEM Infrastructure Server (NIS)
0.6.84-BETA
Verbundener NIS: 
http://localhost:7890/Tried it with safari and chrome
If your nis is stuck, you either should sync from scratch or download a recent db from bob: 
bob.nem.ninja/nis5_mainnet-1002k.h2.db.zipwith nanowallet i wouldnt need NIS anymore, right?
can i trust the actual nanowallet version? is it anyhow more unsecure than the standalone?
with nanowallet i wouldnt need NIS anymore, right?
Not on your local machine. The Nanowallet automatically connects to a node in the NEM network ( at the moment - " 
https://nemnodes.org/monitor/ " - but you can also change it in the upper right corner of the Nanowallet).
can i trust the actual nanowallet version?
Why not. The Nanowallet using the most modern Crypto libraries and don´t send any sensitive data in the Internet. It also has a very high range of functions, it´s very fast and modern. 
Meanwhile it´s the number one. 
So i have to trust the node i connect to. Is there a chance to connect to an "unsafe" node? how can i, as an amateur identify, if the node is trustworthy?