Spam is everywhere, and it's very hard to keep out. Lock your door and it seeps through underneath, through the hinges, even through the keyhole. So the news (on April 1st) that ProBlogger was launching a service called PayPerTweet gave us food for thought, as it were.

Twitter is no stranger to controversy. A teenager on work placement at Morgan Stanley made national news in July this year when he wrote a report about how teens use social network. Teens don't use Twitter; it's for old people, said 15-year-old Matthew Robson. This and other "revelations" seemed to shock some of the great and good at the investment bank (which might suggest they should get out more).

But leaving that aside, millions of people do use Twitter: and ProBlogger looked as though it was trying to cash in on that fact by announcing their new service. PayPerTweet, said ProBlogger, "delivers online word of mouth marketing, brand building and traffic generation" by getting people to tweet for money.

OK, we quickly realised that this was an April Fool. So did many other people. But what is interesting – or alarming – is the number of respondents who thought it was a good idea.

PayPerTweet won't be happening; but something similar might. If not now, then sometime in the not-too-distant future. Perhaps from one of those who thought the spoof was a good idea.

And this raises other questions. Is it too easy to spam Twitter? Will it become spam central? And how will Twitter make money in the future?

Twitter, like all other social presences on the Internet, is changing, evolving before our eyes. Maybe, as Matthew Robson thought, it will just die away as its "old" users die themselves. Maybe it will become something different. But we think it's worth keeping an eye on.