These are the IP addresses from which most of the attacks on the Internet are coming. If you filter these out, you should be appreciably safer. This list is updated regularly (several times a day) and reflects the current state of affairs. However the attackers do switch around and change addresses to avoid detection, so the situation could well be different tomorrow. One strategy is to filter out this list today, then tomorrow etc. add any new addresses to the filter. It's all a great deal of trouble, but filtering out these IP addresses should improve the security of your machine on average.

This list is less useful unless you know what you are doing. The attacks are always made on a specific port (e.g. 80 for http) and using a specific protocol (TCP or UDP). If you have the facility, you can make your filters more specific by including port and protocol. If you don't understand ports and protocols, ignore this list and just filter on IP address.

A final warning. These lists are only the top 10 of hundreds of attacks recorded regularly. Filtering these will not protect you from the 11th. on the list of top offenders.