"#Nike600K," a term being promoted by Nike Corre Brasil, takes the number one position on Twitter on the morning of October 21.

Most tweets with the term "#Nike600K" are in Portuguese. Microbloggers are using their 140 characters to talk about the Nike 600K challenge that sees athletes run 200km per day for three days and can be tracked and watched live online.

In second, third and fourth places are the hashtags "#themwasthedays," "#yeaisaidit" and "#mickyyoochun."

Penthouse magazine founder Bob "Guccione" passed away on October 20 and users are spreading the news with tweets.

News from Apple's "Back to the Mac" press conference, held on October 20, has seen "Mac App," "iLife" and "Apple Killed" shoot into Twitter's trending topics.

The company announced a new version of its iLife software suite, FaceTime for iChat, an Application store for Mac OS X devices and a redesigned line of MacBook Air laptops.

"Yep, Apple Killed The CD Today" tweet users sharing a link to an article from technology blog TechCrunch.

Others are tweeting, "The Mac App Store revolutionizes the way that applications are installed. By doing it the same way that Linux has for years," "Introducing the Mac App Store. Finally, an easy way to bring fart apps to the Mac" and "If the Mac App Store is an optional way to get and install apps, I don't care. If it's the only way, I'll be looking for a new OS."

The death of Ari Up, a British vocalist and member of the punk band the Slits has pushed "Slits" into ninth place while chatter about forthcoming Blu-ray and DVD releases has landed "Blu-ray" in tenth place.

The top 10 most talked about topics on Twitter on October 21 at 7:30 AM GMT are:

  1. #Nike600K (Promoted)
  2. #themwasthedays (new)
  3. #yeaisaidit (new)
  4. #mickyyoochun (new)
  5. Guccione (new)
  6. Mac App (new)
  7. iLife (new)
  8. Apple Killed (new)
  9. Slits (new)
  10. Blu-ray (new)