Not sure if you are correlating hacks happening because they are both 1.5 and locally hosted. The two would be mutually exclusive unless you are stating your suspicions that the hacker is specifically targetting local sites running J! 1.5. In which case I've just wasted text and time... :D
And true, if you are running J1.5, migrate to 2.5 ASAP. Joomla 1.5 reached end of life in April. The last patch v 1.5.26(September), is most likely...eh... THE LAST. If one's site is heavily dependent on, say, a bunch of 1.5 extensions then you will have to go through all the extensions' code testing & fixing vulnerabilities. Its just a timebomb...migrate! I have a client with a 1.5 site and I know I have tonnes of work to do.