strange sub.which.net dialogue box

[Raify]

Why does this window pop up:

[pic]http://photos.fotango.com/p/eba00453953f00000030.jpg[/pic]

when I click on [url]this thread|http://www.pistonheads.com/gassing/topic.asp?t=205909&f=141&h=0&p=2[/url]

:confused: It doesn't look like an advert?

[mmm-five]

Because someone put a link to a picture in the thread which was from a subscriber-based website - you're not that subscriber so it asks you to log on!

[Raify]

Aha! makes sense now, thanks.