People all over the globe today are marking World AIDS Day, with concerts and other events generating awareness for the disease. Seattle entrepreneur and angel investor Mike Koss felt compelled to do his part, so he turned to Twitter for a little philanthropic experiment.

At about 1 p.m. today, the former Microsoft employee posted this short message on his Twitter account: "For each re-tweet, I'll donate $5 to fight AIDS." What happened next surprised Koss, who thought he might generate $500 for AIDS research from his more than 900 followers.

The Tweet went viral. As of 6:45 p.m., Koss' message had been retweeted 1,513 times for a whopping $7,565.

"Wow -- This has taken off faster than I thought!" Koss Tweeted earlier this afternoon. And the retweets kept coming.

Koss even set up a fun interactive page to track the activity in real time, watching the $5 donations add up. By 7:15 p.m. -- as an exhausted Koss prepared to head over to the Ignite Seattle event -- the founder of StartPad.org said he had to bring the project to an end.

"If my AIDS campaign hits $10K - I'm going to have to call UNCLE," he wrote in a recent Tweet. "Everyone has been amazing today! Thanks!"