A database update from AVG over the weekend left users with crippled iTunes installations. According to numerous online reports, the update - which came out on Friday - appears to be mistaking iTunes.dll and iTunesRegistry.dll for a Trojan horse identified as Small.BOG, and thus consigning these files into quarantine. As a result, iTunes will not run, and is not fixable by a reinstall.
After the faulty update was released, users began voicing their complaints on Apple's support page and then turned to AVG's official forums when it was discovered the free antivirus was to blame. In response, AVG published a corrected update, issued a statement on Saturday apologizing for the confusion, and explained how to restore iTunes to normal operation.
This isn't the first time a false positive in AVG has wreaked havoc. Back in November of last year the antivirus software misidentified a key Windows system file as malware, leaving non-English versions of XP unbootable. Its link scanner tool has also been accused of being a huge bandwidth hog and a generator of false web traffic, though this issue has since been addressed by the company.