[ic] bad robots - undefined session ids?

[DB]

I've noticed that when I use top, I sometimes see IC processes with what
looks like an undefined session id.

Ones like this I believe should be robots:
interchange: Store 180.76.5.149 nsession - /page.html

Ones like this I believe should be regular users
interchange: Store 213.108.209.218 WydgPRgP - /page.html

But what about ones like this?
interchange: Store 5.248.13.5  - /scan/se=....

these with an undefined session id often seem to be misbehaving -
bad/evil robots doing many and frequent /scan/... The IPs often seem to
be in Russia, China etc. Anyone have thought about this or how to prevent?

DB