Patching my joomla website (version 2.5), to prevent Malware from showing

Hello free lance guys, I have an e commerce website running on joomla version 2.5. I have this problem that it is showing Malware to some of my users, with wording such as "Canadian viagra" with links being shown to some users. I need this cleared up, that's all. My website is [login to view URL] (as mentioned malware is not shown to all users, so you may or may not see it). Important notes: Terms of payment - I will only pay you 30 days after completing my work. Reason is because I need to make sure there is no reoccurence of the malware. The previous free Lancer, velsoft, simply deleted away the bad files, but soon after my website had the same problem. If you do not like this term, DO NOT BID. Basically I just want to pay for results upgrading to newer version of joomla - included in this project will be updating to latest version of joomla 2.5. If you feel upgrading to an even more updated version of joomla, include this in your bid (and include the price as well). Most important is virtuemart works in similar capacity as currently running. Other components are not as critical Point of entry - the malware is obviously coming in from some loophole in the joomla system, so as the professional in the matter, you are to advise me which modules to keep, delete or to leave as is. Also any advise from you to prevent future reoccur ancestors is appreciated. Thank you for your time and good luck bidding, if I like your bid I will contact you shortly after the bidding phase is over to get the project started. So remember, I am paying for results, not for work put in, if you cannot solve my problems, don't waste both our time and do not bid.