Threat Level: ORANGE

Don't want online ad companies shadowing you across the Web? Simply delete their browser tracking cookies, and you're free to wander. Right? Wrong. Web advertisers have found a way to follow you anyway, using after you delete them--hence their nickname, zombie cookies.

Last summer, privacy attorney against ABC, Disney, MTV, NBC, and their advertising partners, charging them with violating federal privacy and computer security laws via Flash cookies.

The solution: You can use Adobe's occasionally flaky , the Firefox plug-in , or to . The problem? Sites such as Pandora Radio and YouTube rely on Flash cookies--which can store up to 100KB of data--to improve media playback, and they may not work without them. So choose your undead victims with care.