The spam you received was an advertisement for a (now removed) porn site. This was, to the best of my knowledge, the first commercial Bebo spam – if you come across any others let me know.
Just like email, the Bebo message system provides unscrupulous advertisers with an opportunity to send hundreds or thousands of unsolicited messages, almost certainly automatically, and very cheaply. If even a small number of these messages result in sales, bingo the bad guys make money.
You can do your part to prevent messages like this in the future by contacting Bebo directly, reporting the message you received, and requesting they remove the ‘feature’ that allows sending a large amount of Bebo mails to users not on your friends list. Such messages explicitly violate Bebo’s terms of service.
Although the message you received cannot itself harm your computer, sites like the one it linked to can contain Trojan virus’s, which could infect your PC. To protect against such threats, always use a safe web browser, like Firefox 2; install antivirus software, like AVG antivirus; and firewall software, like Zonealarm.
If you’re afraid your machine may have already become infected, run an antivirus scan, then download and run an anti Spyware package; Spybot, and Ad Aware are both free and good.
Finally, never use your credit card on a site which is not trustworthy. If in doubt, use a third party service like Pay Pal or Google Checkout; which will minimize your potential losses to the individual payment made.
Hope this helps. See you on Bebo.