The makers of the Bitcoin software warn their users against that since July 4, some miners dig invalid blocks. Thanks outdated wallets arises the risk of invalid certificates for users of crypto currency. But there are workarounds.
The problem concerns mainly the users of wallets that rely on a simplified payment method (SVP, Simplified Payment Verification), according to a warning. These include Multibit, Electrum and Bitcoin Wallet for Android. Users of such wallets recommend the developer to wait an additional 30 confirmations of payment, to make sure that it is not a bad block. The recommendation is also aimed at users of web wallets and those that use “bitcoin-core 0.9.4″ or earlier versions. From “bitcoin-core 0.9.5″ no longer exists the problem, however.
In response to the invalid blocks formed according to announcement of Bitcoin developers from 5 July a new Fork, which is the strongest chain now. However, the developers give the time being no clear, in terms of number of confirmations. A list of hashes of the invalid blocks provides the Bitcoin wiki.