I downloaded about fifty JPEGs with Shareaza 2.5.2.0 during the past two or three hours. I'm pretty sure they all showed a green Completed, Verified in the downloads window when done. Despite this, one of them appears to have been corrupt: Windows Explorer would not thumbnail it, the picture and fax viewer would not view it, and Photoshop CS2 would not open it.
That's not supposed to be theoretically possible, is it? If it shows Completed, Verified the file as received should be a bit-identical copy of the file as transmitted. The odds against a chance hash collision making a file seem ok that actually was corrupted are literally astronomical, even if Shareaza weren't potentially checking it with three or four differently-calculated hashes. SHA-1 alone, with 2^160 hashes, gives odds scarcely better than one in a googol of this happening.
On the other hand, the file obviously was corrupted in transit; there's no reason for someone to be intentionally sharing (or even keeping) a jpeg that is broken for whatever reason. (There are spammers sharing intentionally broken music files, but jpegs? And it had a single, fairly slow source and generally looked like a legitimate hit. Spams tend to be easy for an experienced user to spot and tend to have several sources and download, if at all, lightning-fast, since the spammers tend to have a high capacity server farm. Furthermore, the only image search spams I've seen in years of using Gnutella have been images that are actually ads, deliberately mislabeled as something else, or copies of legitimate images that have been altered to add an ad banner or similarly.)
This suggests the possibility of a bug in Shareaza's hashing, or that can cause it to skip the integrity check from time to time but still report a file as Verified.