My blog was hacked and now has hidden links throughout

About a month ago, I discovered than an old blog post had been riddled with hidden links to porn and spam sites. After investigating further, I discovered similar links on most of my older posts — meaning that my site had somehow been hacked by a spammer. After upgrading to WP 2.5 (from 1.9 I think) I hoped the links would be automatically removed, but they weren;t. To manually remove them from 1500 or so older posts is unfathomable to me. Are there automated ways to remove hidden links?