It seems some fake 3.55 CFW is spreading around the web.
This News was posted on Logic-Sunrise site:
A fake CFW 3.55 jailbreak has geen circulating on the net for some hours, the person puts his CFW to a release from the team PS3USBJailbreak. The archive contains the following files PS3UPDATE.rar: File word.txt, PS3UPDATE.PUP, PUPsigner.exe.
The MD5 hash of the file. PUP is B819861F75D50882142CBEC8A F54B00012BC049D and therefore it is in fact the official 3.50 FW.
And certainly that. exe file contains a virus / trojan.
!! UNDER NO CIRCUMSTANCES USE THIS UPDATE !!!!!
You can find the real one here