I surfed over to Yahoo! (NASDAQ:YHOO) this weekend and was surprised to see some intrusive online advertising rear its ugly head again. Most of the text headers on the landing page for the site's weekend financial section had hyperlinked "3"s where the letter "e" should be -- like w33k3nd instead of weekend. After you clicked on any of those links, you would find yourself at a page pitching the new BMW 3 Series.

The transformation makes more sense when you see the animated graphic ad on the page -- a sleek black BMW coupe driving into a line of threes, sending them flying off the ad box -- it brought back some memories.

A few years ago, when ING (NYSE:ING) was rolling out its ING Direct money market accounts, we here at Fool.com struck a marketing deal with the company that found some of our online content tweaked in a similar way. Words ending in the "ing" suffix were transformed into hyperlinks to the global financial-service giant's savings center.

The reactions -- from our readers and our editorial staff alike -- were passionately mixed. But whether you love or hate these kinds of ad placements, you have to wonder about the timing of similar deals these days. We were in more innocent times back then. These days, when I see unexpected links, I begin to wonder whether the site has been hijacked or if I contracted a nasty adware virus along the way.

I applaud marketing creativity, but it can be taken too far. The reason that Microsoft (NASDAQ:MSFT) is losing Internet Explorer market share to Mozilla these days is because Web browser spyware can really kill the Internet experience, and keeping your system clean is critical.

Most of us realize that enjoying free Internet content means welcoming a wide range of advertising styles. While I am more a fan of the passive yet relevant contextual ad blocks -- like those that Yahoo! has put out since its acquisition of Overture -- I can understand why companies like Fastclick (NASDAQ:FSTC) and ValueClick (NASDAQ:VCLK) are trying out some innovative new concepts.

Yet as long as I am suspicious of where my computer's been, please, Yahoo!, leave my "e"s alone.

Too cheap to buy a vowel? Try these on for size:

Longtime Fool contributor Rick Munarriz was the middle of 3 children. He's all for clever marketing, but he does not own shares in any of the companies mentioned in this story. The Fool has a disclosure policy. He is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early.