There is no trojan in messenger plus!, it is a false detection, I assume that you're using AVG, which detects Messenger Plus! as this. Allow it to install.
msngplus 3 - by Darth Mitch on 08-09-2005 at 06:59 PM RE: msngplus 3 - by user27089 on 08-09-2005 at 07:03 PM RE: msngplus 3 - by Darth Mitch on 08-09-2005 at 07:09 PM RE: msngplus 3 - by user27089 on 08-09-2005 at 07:10 PM RE: msngplus 3 - by absorbation on 08-09-2005 at 07:10 PM RE: msngplus 3 - by Darth Mitch on 08-09-2005 at 07:14 PM RE: msngplus 3 - by user27089 on 08-09-2005 at 07:16 PM RE: msngplus 3 - by Darth Mitch on 08-09-2005 at 07:19 PM RE: msngplus 3 - by absorbation on 08-09-2005 at 07:26 PM RE: msngplus 3 - by Darth Mitch on 08-09-2005 at 07:32 PM RE: msngplus 3 - by user27089 on 08-09-2005 at 07:36 PM RE: msngplus 3 - by Darth Mitch on 08-09-2005 at 07:37 PM RE: msngplus 3 - by absorbation on 08-09-2005 at 07:58 PM RE: msngplus 3 - by matty on 08-09-2005 at 08:02 PM
