This year, spim--spam over IM--messages will number about 2 billion, four times last year's total, according to David Ferris, president of Ferris Research.

Many spim messages tout pornography or fast-money schemes, and include a link to a Web site. Following that link can trigger an avalanche of other privacy and security problems: You may get swamped with pop-up ads, or spyware and Trojan horse apps may install themselves on your PC. And spim can be even more intrusive than spam. Just like a regular IM message, spim can pop up in a chat window on top of whatever you're working on at the time.

Fortunately, all major instant messaging packages let you limit or eliminate spim, but the settings that block it require you to make some trade-offs. Messages from people not on your contact list will be blocked. You'll still be able to add users to your buddy list, but it'll take a few more mouse clicks. It's a good idea to add everyone you think you may want to communicate with to your list before you implement the following tips.

ICQ: Click the Main button, and select Security and Privacy Permissions. Click Communication Events in the left pane, and then fill in the radio buttons under either the yellow check mark icon (which limits these actions to users on your contact list) or the red X icon (which prevents anyone from sending you these things). Click Spam Control in the left pane, fill in all the check boxes in the right pane, and choose All users next to the item labeled 'Do not accept Multi Recipient Messages from'.

AOL Instant Messenger: Press the F3 key (or click My AIM, Edit Options, Edit Preferences) to open the preferences window. Select Privacy in the left pane, and then choose the Allow only users on my buddy list option under the 'Who Can Contact Me' header.

Yahoo Messenger: Click the Login menu and choose Preferences. Select the Privacy item in the left pane of the Yahoo Messenger Preferences window, and choose Ignore anyone who is not on my Friend list. To prevent spim through Yahoo's Web interface, choose Do not allow users to see me online and contact me in the 'When people see my ID on Yahoo Web sites' section.

MSN Messenger: Once you're logged in, click Tools, Options, and then select the Privacy tab. Fill in the Only people on my Allow List can see my status and send me messages check box. The Privacy tab also has controls for adding or removing people on the Allow List, as well as a button that lets you see which other MSN Messenger users have added you to their contact list.

You can e-mail Brandt at privacywatch@pcworld.com.