You are right! There are several methods by which viruses can be used to target cancer (target specific or not), so I have changed the start of my reply to be more accurate and polite :) cheers

There are in fact ways to modify viruses to make them preferentially target cancer cells in a more "general" or non-specific way (the technical term would be antigen-agnostic).

• These viruses are known as oncolytic viruses and are a major field of study in cancer immunotherapy/virotherapy. Many of these viruses are rhabdoviruses (same family as rabies, but obviously not rabies), vaccinia viruses (pox viruses), or herpes viruses. Every nucleated cell in the body has an internal anti-viral response that result in expression of viral-response genes to alter the cell (such as initiating cell death to prevent virus spread) and release interferon proteins to alert the immune system and prime antigen-presentation.

Many cancer cells actually have disruptions and mutations in these pathways so that they do not have as robust an anti-viral response. This can be exploited with oncolytic viruses.

To exploit this the virus can be genetically engineered to lack its own anti-immune system genes that interact with those interferon response genes.

• For example, VSV (a rhabdovirus) can be modified with a mutant M gene so that it is more sensitive to the interferon proteins and response pathways. So using such a virus, normal healthy cells which have a proper anti-viral response can be infected by this VSV M-mutant but it is not productive and the virus wont replicate more than once in those tissues. However in cancer cells with the defective interferon pathways, the viruses does attain productive replication and can kill the tumor cell.

• The second important aspect of this is the virus alerts the host immune system to its presence within the tumor, results in spreading of mutated antigens from the tumor, and can then trigger a stronger immune response against the tumor itself. This is a huge field and is leading to oncolytic viruses as a vector for both direct anti-tumor toxicity and immunotherapy/vaccination.

There is currently 1 FDA approved oncolytic virus treatment: T-vec

My research is not on oncolytic viruses but I have some knowledge, the modern space of oncolytic viruses has likely advanced quite a bit and other viruses may be better choices than say VSV.

Source: PhD in immunology. For further reading refer to these articles

Oncolytic viruses for cancer immunotherapy

Engineering strategies to enhance oncolytic viruses in cancer immunotherapy

Vesicular stomatitis virus as a flexible platform for oncolytic virotherapy against cancer