I"m running FC6 and the logwatch that is generated each day had the following entry in it:

**Unmatched Entries**
reverse mapping checking getaddrinfo for 201-91-155-2.customer.tdatabrasil.net.br failed - POSSIBLE BREAK-IN ATTEMPT! : 4 time(s)

1. What does this mean?
2. Is there a way to prevent it?

I keep my system updated with yum weekly and have denyhosts running.

Thanks.