Temporary Restrictions

If you receive the message that you are temporarily restricted or unable to connect, the first step is to attempt to log onto another realm, for instance if you are on Europe (Northrend), attempt to log onto USWest (Lordaeron).
If you cannot access only one realm then you may have a temporary IP restriction.

Possible causes for temporary restrictions include:

All Games:
Spamming text or chat commands such as /friends list or /whisper or /whois (often associated with bots).
Rapidly connecting/disconnecting to/from Battle.net - over 50 connections/hour (often associated with bots or switching between characters).
Viewing multiple profiles in a very short time period.
Exceeding 8 connections to Battle.net (often associated with bots).
Repeated use of an incorrect password may lock an account login for your protection.
Use of third-party/add-on programs (hacks) - these include but are not limited to sending bad packets, flooding the server(s), and the use of hack programs.

Diablo II Only:
Scrolling through skill selection using the mouse wheel.
Going in and out of accounts/characters too quickly. i.e Muling
Going in and out of games too quickly (most common cause). i.e. Muling, magic finding, Baal/Pindleskin runs, etc.
Repeated requests for a new screen to see what you wish to gamble for.
Going up and down a way point to refresh the screen in a shop (see above).
Repeated use of a spell with no cast delay such as Amplify Damage or Glacial Spike. This lasts a maximum of 12 hours.

Restrictions lasting longer than 72 hours usually indicates that you were witnessed by a Battle.net representative doing something against the Terms of Use Agreement, which warranted a lengthy restriction. These restrictions will be for connecting to the realm at all.

Common causes for extended restrictions include, but are not limited to:
Excessive spamming or flooding in a channel (often associated with bots).
Spamming over multiple channels - even if it is just one line per channel. (often associated with bots).
Use of flood or load bots.
Harrassment of another player and/or clan.
Advertisement of an inappropriate website URL.
Use of third-party/add-on programs (hacks) - these include but are not limited to sending bad packets, flooding the server(s), and the use of hack programs.
This type of restriction can last up to 2 weeks.

Unfortunately, you will have to wait it out or obtain a different IP address from which to play. Please note that we will not provide support for changing your IP address.

If you are absolutely certain you did not spam, keep in mind that anyone behind your network, or if your ISP shares your IP address (as in more than one persons are given the same IP address), gets restricted from battle.net, you will suffer the penalties along with them.
This is the unfortunate disadvantage of using a shared IP address.
Also, keep track of siblings and other people with access to your computer and/or network who play on Battle.net, as they can get you restricted as well.
It is also possible that your computer may be infected with a virus that has resulted in the restriction.

It is important to realize that these restrictions are not exactly a punishment, but rather that they are necessary for server stability. When you spam, it places a much heavier load on the server and ruins the gameplay experience for everybody.