what do you do when you have attempted hacks in your logs

[Dave Smith <dms121_(_at_)_yahoo_(_dot_)_com>]

I check my logs regularly and there is often hundreds
of hack attempts, though none successful. I usually do
a lookup on the IP, which gives little useful
information. What do you guys do? Ignore them? Attempt
to contact somone at the domain? whois often gives me
nothing, nslookup gives a bit more, but often not
enough. I always add the IP to my block list, but
that's about it....

looking for advice....

thx
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