wallet.dat changes?

[wool]

Hello.

Why is the wallet file modified after every run of Bitcoin, even though I haven't sent/received any bitcoins or modified addresses?

[chrisrico]

Other information is stored in the wallet other than your keys. Application settings, last seen block number, transactions. If you downloaded any blocks, then at the very least the wallet will be updated with the number of the block that was last scanned for transactions. This is to make startup quicker.