T4/T5 is a bootleg version of T3, full of spyware and lacking most of the security features of T3. T3 is a client modification which enables all of the admin features inside of the IMVU client and disables all of the tracking features that IMVU staff uses to spy on their customers / catch people who break their TOS. T4 is a bootleg of the same thing, which enables some of the admin features (not all) and skips disabling the tracking features ... allowing IMVU staff to still spy on you while you break their terms of service. T3 is a useful and safe / recommended tool. T4 is useful, but less useful than T3 and is not safe.
The official IMVU client by default contains spyware that steals a little over 120 different pieces of personal information from the user's computer. (first name, last name, address, phone number, hardware ID's, software licenses, agent data, geo location, ip address, account names, chat logs, product usage logs ... etc) every time you login, and every time the client crashes. IMVU inc sells this information to third party marketing companies, as well as uses the data to spy on their users ... to detect, track, and go after users who break their terms of service. (example: sex product users)
T3 has this spyware stripped out, to protect users. T4 leaves the spyware in, leaving the user vulnerable to waves of periodic banning and hardware bans (similar to an account ban, but hits all of your accounts, not just one).
T3 can be purchased from Datamine:
ucp.php?i=pm&mode=compose&u=18313