version.php is required for all plugins but themes.
$plugin->version = 2011051000;
$plugin->requires = 2010112400;
$plugin->cron = 0;
$plugin->component = 'plugintype_pluginname';
$plugin->maturity = MATURITY_STABLE;
$plugin->release = '2.x (Build: 2011051000)';
$plugin->dependencies = array('mod_forum' => ANY_VERSION, 'mod_data' => 2010020300);
Replace $plugin with $module for activity modules, as in
$module->version = 2012122400;